Immobilized algae ball, preparation method thereof and immobilized algae ball and bacterium symbiotic system

Abstract

The invention provides an immobilized algae ball, a preparation method thereof and an immobilized algae ball and bacterium symbiotic system, and belongs to the technical field of sewage treatment, and the preparation method comprises the following steps: taking a chlorella culture solution, centrifuging to obtain concentrated chlorella, mixing the concentrated chlorella with deionized water to obtain an algae solution, preparing a sodium alginate solution at the same time, and adding the sodium alginate solution into the algae solution; uniformly mixing the algae solution with the sodium alginate solution to obtain a mixed solution; preparing a CaCl2 solution, slowly dropwise adding the mixed solution into the CaCl2 solution, carrying out immobilized cross-linking at room temperature for 23-25 hours, and washing with deionized water to obtain the algae balls. The algae balls are prepared by adopting a sodium alginate-calcium chloride embedding method, the concentration and crosslinking time of sodium alginate and calcium chloride are optimized, the immobilization of chlorella is realized, nitrogen and phosphorus in sewage can be effectively removed by the algae balls and a suspended sludge system, and the algae balls can be recycled after sewage treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to an immobilized algae ball and a preparation method thereof, and an immobilized algae ball and bacteria symbiotic system. Background Art

[0002] Biological treatment is one of the main methods currently widely used to treat urban domestic sewage, including activated sludge method, biofilm method and other process forms. However, traditional sewage treatment processes generally have problems such as high energy consumption, high operating costs, complex processes and difficulty in regulation. Therefore, it is of great significance to develop new sewage treatment technologies with high treatment efficiency and low operating costs that can be widely promoted and applied in cities.

[0003] The bacteria-algae symbiotic system has the advantages of fast microbial reproduction, high photosynthetic rate, and strong environmental adaptability. The system is mainly composed of microalgae and activated sludge. Microalgae produce O2 through photosynthesis, thereby reducing or replacing the demand for mechanical aeration of activated sludge, while absorbing a large amount of nitrogen and phosphorus to maintain its own growth and proliferation; activated sludge can degrade organic matter in sewage, produce CO2 or simple organic matter, and provide nutrients for algae cells to absorb and utilize, thus forming a mutually beneficial symbiotic relationship between microalgae and activated sludge.

[0004] Compared with free algae, immobilized algae have advantages such as high biological concentration, easy harvesting of algae cells, higher removal effect of nitrogen and phosphorus nutrients, and stronger adaptability to pH, temperature, pollutant concentration and complex microecological environment. The method of using immobilized algae can well solve the problems of bacterial algae separation and algae cell loss, and can also recycle immobilized algae to reduce the economic cost of sewage treatment process and provide convenience for continuous large-scale sewage treatment.

[0005] At present, there are also studies on the removal of nitrogen and phosphorus from sewage using immobilization methods. Most of them involve single or mixed immobilization of algae and bacterial species. The effect of the inoculation ratio of immobilized algae balls on the removal of nitrogen and phosphorus in sewage treatment by the bacteria-algae symbiotic system is still unknown. Summary of the invention

[0006] In view of the technical problems existing in the background technology, the present application provides an immobilized algae ball and a preparation method thereof, and an immobilized algae ball and bacteria symbiotic system, aiming to solve the technical problem that the inoculation ratio of the immobilized algae ball has an unknown effect on the denitrification and phosphorus removal of wastewater in the bacteria-algae symbiotic system.

[0007] In a first aspect, the present invention provides a method for preparing an immobilized algae ball, comprising the following steps: S1. Take a culture solution of Chlorella in the logarithmic growth phase, centrifuge to obtain concentrated Chlorella, mix the concentrated Chlorella with deionized water to obtain an algae solution, prepare a sodium alginate solution, and mix the algae solution and the sodium alginate solution evenly to obtain a mixed solution; S2. Prepare CaCl2 solution, slowly add the mixed solution into the CaCl2 solution, immobilize and cross-link for 23 to 25 hours at room temperature, and then wash with deionized water to obtain the algae ball.

[0008] In the technical solution of the embodiment of the present application, the sodium alginate-calcium chloride embedding method is used to prepare the algae ball, and the concentrations of sodium alginate and calcium chloride and the cross-linking time are optimized to achieve the immobilization of Chlorella.

[0009] Preferably, the concentration of the algae liquid in step S1 is 8.5-9.5 g / L.

[0010] Preferably, the concentration of the sodium alginate solution in step S1 is 40 g / L.

[0011] Preferably, in step S1, the algae liquid and the sodium alginate solution are uniformly mixed in a volume ratio of 1:(2-3).

[0012] Preferably, the concentration of the CaCl2 solution in step S2 is 20 g / L.

[0013] In a second aspect, an embodiment of the present application provides an immobilized algae ball prepared according to the above method.

[0014] In a third aspect, an embodiment of the present application provides a symbiotic system of immobilized algae balls and bacteria, including algae balls and an activated sludge mixture.

[0015] Preferably, the activated sludge is short-cut nitrification sludge, and the activated sludge concentration is 1.0 g / L.

[0016] Preferably, the mass ratio of activated sludge to algae balls is 1:(0.5~1).

[0017] In the fourth aspect, an embodiment of the present application provides an application of an immobilized algae ball and bacterial symbiotic system in sewage treatment, comprising the following steps: adding an algae ball and an activated sludge mixture to the sewage, aerating the sewage for 5 hours under light conditions, with an aeration flow rate of 0.9~1.0 L / min, adding an organic carbon source to the sewage after the 5th hour of reaction and stopping aeration, and continuing the reaction for 5 hours; microfiltration is performed after the reaction is completed, and the sewage treatment is completed.

[0018] In the technical solution of the embodiment of the present application, enriched short-range nitrification sludge is used as inoculated sludge, algae balls and short-range nitrification sludge are added to the reactor, light is provided on both sides of the reactor, and magnetic stirring is performed at the bottom of the reactor to construct a bacterial-algae symbiotic system. The reactor is used to treat sewage containing ammonia nitrogen and phosphate, and the ammonia nitrogen and phosphate are converted or absorbed by the algae balls and active microorganisms in the sludge. After the reaction is completed, the algae balls can be taken out from the mixed system and recycled.

[0019] Different from the existing technical solutions, the beneficial effects of this application include: The present application uses a sodium alginate-calcium chloride embedding method to prepare algae balls, and optimizes the concentration of sodium alginate and calcium chloride and the cross-linking time to achieve the immobilization of Chlorella. The enriched short-range nitrification sludge is the inoculated sludge, and the algae balls and the short-range nitrification sludge are added to the reactor, light is provided on both sides of the reactor, and magnetic stirring is performed at the bottom of the reactor to construct a bacterial algae symbiotic system. The algae ball and suspended sludge system can effectively remove nitrogen and phosphorus in sewage; the algae-bacteria ratio of 1:1 has the best nitrogen and phosphorus removal effect, and the phosphate removal rate is very high; the algae balls can be recycled after sewage treatment.

[0020] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 It is a comparison chart of ammonia nitrogen and inorganic nitrogen removal rates in Examples 1-2 and Comparative Example 1; Figure 2 It is a graph showing the change in phosphate removal rate in Examples 1-2 and Comparative Example 1; Figure 3 This is a microscopic image of the external morphology of the algae ball in Example 1 magnified 35 times; Figure 4 This is a microscopic image of the external morphology of the algae ball in Example 1 magnified 500 times. DETAILED DESCRIPTION

[0023] The following embodiments of the technical solution of the present application will be described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0025] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0026] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0027] At present, there are also studies on the removal of nitrogen and phosphorus from sewage using immobilization methods. Most of them involve single or mixed immobilization of algae and bacterial species. The effect of the inoculation ratio of immobilized algae balls on the removal of nitrogen and phosphorus in sewage treatment by the bacteria-algae symbiotic system is still unknown.

[0028] In order to solve the technical problem that the effect of immobilized algae inoculation ratio on nitrogen removal and phosphorus removal in sewage treatment by bacteria-algae symbiotic system is still unknown, the present application provides a method for preparing immobilized algae balls, comprising the following steps: S1. Take a culture solution of Chlorella in the logarithmic growth phase, centrifuge to obtain concentrated Chlorella, mix the concentrated Chlorella with deionized water to obtain an algae solution, prepare a sodium alginate solution, and mix the algae solution and the sodium alginate solution evenly to obtain a mixed solution; S2. Prepare CaCl2 solution, slowly add the mixed solution into the CaCl2 solution, immobilize and cross-link for 23 to 25 hours at room temperature, and then wash with deionized water to obtain the algae ball.

[0029] In the technical solution of the embodiment of the present application, the sodium alginate-calcium chloride embedding method is used to prepare the algae ball, and the concentrations of sodium alginate and calcium chloride and the cross-linking time are optimized to achieve the immobilization of Chlorella.

[0030] Preferably, the concentration of the algae liquid in step S1 is 8.5-9.5 g / L.

[0031] Preferably, the concentration of the sodium alginate solution in step S1 is 40 g / L.

[0032] Preferably, in step S1, the algae liquid and the sodium alginate solution are uniformly mixed in a volume ratio of 1:(2-3).

[0033] Preferably, the concentration of the CaCl2 solution in step S2 is 20 g / L.

[0034] In a second aspect, an embodiment of the present application provides an immobilized algae ball prepared according to the above method.

[0035] In a third aspect, an embodiment of the present application provides a symbiotic system of immobilized algae balls and bacteria, including algae balls and an activated sludge mixture.

[0036] Preferably, the activated sludge is short-cut nitrification sludge, and the activated sludge concentration is 1.0 g / L.

[0037] Preferably, the mass ratio of activated sludge to algae balls is 1:(0.5~1).

[0038] In the fourth aspect, an embodiment of the present application provides an application of an immobilized algae ball and bacterial symbiotic system in sewage treatment, comprising the following steps: adding an algae ball and an activated sludge mixture to the sewage, aerating the reaction for 5 hours under light conditions, with an aeration flow rate of 0.9~1.0 L / min, adding an organic carbon source to the sewage and stopping aeration after the reaction reaches the 5th hour, and continuing the reaction for 5 hours; microfiltration is performed after the reaction is completed, and the sewage treatment is completed.

[0039] In the technical solution of the embodiment of the present application, enriched short-range nitrification sludge is used as inoculated sludge, algae balls and short-range nitrification sludge are added to the reactor, light is provided on both sides of the reactor, and magnetic stirring is performed at the bottom of the reactor to construct a bacterial-algae symbiotic system. The reactor is used to treat sewage containing ammonia nitrogen and phosphate, and the ammonia nitrogen and phosphate are converted or absorbed by the algae balls and active microorganisms in the sludge. After the reaction is completed, the algae balls can be taken out from the mixed system and recycled.

[0040] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be obtained commercially.

[0041] 1. Preparation method Example 1 An immobilized algae ball, the preparation method is as follows: 1.1 Reagent preparation (1) Sodium alginate solution: Weigh 40 g of sodium alginate powder, mix it with an appropriate volume of distilled water, and dissolve it in a 100°C boiling water bath to obtain a 4% (w / v) sodium alginate solution. Sterilize the solution and cool it for later use.

[0042] (2) CaCl2 solution: Weigh 20 g of CaCl2 and dissolve it in an appropriate volume of distilled water to obtain a 2% (w / v) CaCl2 solution. Place the solution in a 4°C refrigerator and keep it refrigerated for later use.

[0043] 1.2 Collection of Chlorella Take some culture medium of Chlorella in the logarithmic growth period, place it in a high-speed desktop centrifuge, centrifuge it at 4000 rpm for 10 min, replace the supernatant with deionized water, mix it evenly, measure the concentration of the algae solution (burning temperature 105 ℃), dilute the algae solution concentration to 9 g / L, take an appropriate volume of algae solution, and mix it evenly with sodium alginate solution at a volume ratio of 1:2 (algae solution: sodium alginate).

[0044] 1.3 Preparation of algae balls Inject the mixture of Chlorella and sodium alginate into a 10 mL syringe, and take an appropriate volume of CaCl2 solution into a beaker, and stir slowly and continuously with a magnetic stirrer. Slowly drip the mixture of Chlorella and sodium alginate 15 cm above the surface of the CaCl2 solution to obtain an algae ball with a diameter of 3-4 mm and a weight of about 0.03 g. At 25 °C, the algae ball was fixed and cross-linked for 24 h, rinsed three times with deionized water to remove the residual CaCl2 liquid, and then added with BG11 medium and stored in a 250 mL conical flask, and placed in a constant temperature and light incubator for use.

[0045] 2. Constructing the bacterial-algal mixture Before the experiment, an appropriate amount of fresh short-range nitrification sludge was washed three times with deionized water to remove residual impurities in the sludge mixture, and the sludge concentration was measured (ignition temperature 550 ℃). According to the sludge concentration of 1.0 g / L set in the experiment, an appropriate amount of sludge was taken, and algae balls were added according to the mass ratio of sludge to algae of 1:0.5 to obtain a bacteria-algae mixture.

[0046] 3. Build the reactor The reactor was built using a 500 mL conical flask with a screw cap. LED full-spectrum lamps were used on both sides of the conical flask to provide illumination. The distance between the reactor and the lamp was adjusted to provide 4000 lux of illumination to the reactor sidewall. A magnetic stirrer was used to mix the algae balls and sludge at the bottom of the reactor. A metal feeder was added to the center of the top screw cap. An aeration tube was used to connect the small hole above the feeder to the aeration pump and gas flow meter. The aeration tube was then used to connect the small hole below the feeder to the bubble stone. Air passed through the bubble stone to form microbubbles in the sludge mixture. The microbubbles provided oxygen when they rose in the water for microorganisms to use.

[0047] 4. Preparation of synthetic wastewater Artificial synthetic sewage was prepared, the components of which were: 454 mg / L NH4Cl (ammonia nitrogen concentration 120 mg-N / L), 788 mg / L NaHCO3, 64 mg / L K2HPO4 and 64 mg / L KH2PO4 in phosphate buffer, 1013 mg / L sodium acetate (COD concentration 790 mg / L), and a mixture of trace elements.

[0048] 5. The nitrogen and phosphorus in the sewage were removed by using the bacteria-algae mixed solution prepared in Example 1, and the sewage was treated according to the following steps: Assemble the reactor, turn on the power of the lamp tube to provide light to the side wall of the reactor, add algae balls and activated sludge, and then add artificial synthetic sewage except sodium acetate. Turn on the power of the magnetic stirrer, set the stirring speed to 250 rpm, turn on the power of the aeration pump, provide oxygen to the microorganisms, and treat artificial synthetic sewage. The total reaction time is 10 h. Keep the aeration pump working from 0 to 5 h. The gas flowmeter controls the aeration flow rate to 1 L / min. Turn off the aeration pump from 5 to 10 h, and add sodium acetate to the sewage in the 5th hour. After filtering through a 0.22 μm polyethersulfone filter membrane, the sewage treatment is completed.

[0049] Example 2 The difference between Example 2 and Example 1 is that algae balls are added in a mass ratio of 1:1 between sludge and algae to obtain a bacteria-algae mixed solution, which is used to treat nitrogen and phosphorus in sewage, and the other steps are the same as in the example.

[0050] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that no algae balls are added, activated sludge is used to treat nitrogen and phosphorus in sewage, and the other steps are the same as those in the example.

[0051] 2. Test Method 1. Morphology test method of algae balls After using algae balls and suspended sludge to treat sewage, the algae balls were collected into centrifuge tubes and tested with SEM to observe the morphology of the algae balls. The specific method was: wash twice with 0.1M PBS buffer, discard the solution, slowly add 2.5% glutaraldehyde fixative precooled at 4°C along the tube wall, and then store it in a 4°C refrigerator for 12 hours. The Science Compass research service platform was commissioned to test the SEM and take photos of the external microscopic morphology of the algae balls.

[0052] 2. Ammonia nitrogen removal rate test method Take an appropriate amount of water sample at the 0th hour and after the end of the experiment, refer to the "Determination of Ammonia Nitrogen in Water Quality - Nessler's Reagent Spectrophotometry (HJ 535-2009)", add it to a 50mL colorimetric tube, dilute to the mark, add 1.0mL potassium sodium tartrate solution, mix well, add 1.0mL Nessler's reagent, mix well, let stand for 10 minutes, and measure the absorbance at 420nm with a UV spectrophotometer. Calculate the ammonia nitrogen content of the sample using the ammonia nitrogen standard curve. The ammonia nitrogen removal rate is the ratio of the ammonia nitrogen removal before and after the experiment to the ammonia nitrogen content of the original water sample.

[0053] 3. Test method for inorganic nitrogen removal rate Inorganic nitrogen includes ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen. The inorganic nitrogen removal rate test involves the determination of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen, referring to "Water Quality Ammonia Nitrogen Determination Nessler Reagent Spectrophotometry (HJ 535-2009)", "Water Quality Nitrate Nitrogen Determination Ultraviolet Spectrophotometry (Trial) (HJ / T 346─ 2007)", and "Water Quality Nitrite Nitrogen Determination Spectrophotometry (GB 7493-87)".

[0054] ① The test operation steps for ammonia nitrogen are as described in 2. Ammonia nitrogen removal rate test method.

[0055] ② The determination method of nitrate nitrogen is as follows: Take an appropriate amount of water samples at 0 h and after the end of the experiment, refer to the "Determination of Nitrate Nitrogen in Water Quality - Ultraviolet Spectrophotometry (Trial) (HJ / T 346─ 2007)", add to a 50 mL colorimetric tube, dilute to the mark, add 1.0 mL of 1 mol / L hydrochloric acid solution, mix well, add 100 μL of aminosulfonic acid, mix well, and use an ultraviolet spectrophotometer to measure the multi-wavelength absorbance at 220 and 275 nm. The nitrate nitrogen content of the sample is calculated using the nitrate nitrogen standard curve. The nitrate nitrogen removal rate is the ratio of the nitrate nitrogen removal before and after the experiment to the nitrate nitrogen content of the original water sample.

[0056] ③ The determination method of nitrite nitrogen is as follows: Take an appropriate amount of water samples at the 0th hour and after the end of the experiment, refer to the "Spectrophotometric method for the determination of nitrite nitrogen in water quality (GB 7493-87)", add it to a 50 mL colorimetric tube, dilute to the mark, add 1.0 mL of color developer, mix well, let it stand for 20 min, use an ultraviolet spectrophotometer to measure the absorbance at 540 nm, and use the standard curve of nitrite nitrogen to calculate the nitrite nitrogen content of the sample. The nitrite nitrogen removal rate is the ratio of the nitrite nitrogen removal before and after the experiment to the nitrite nitrogen content of the original water sample.

[0057] 4. Phosphate removal rate test method Take an appropriate amount of water sample at 0 h and after the end of the experiment, refer to the "Determination of Total Phosphorus in Water Quality - Ammonium Molybdate Spectrophotometry (GB 11893-89)", add to a 50 mL colorimetric tube, dilute to 25 mL, add 4 mL potassium persulfate solution for digestion, then add 1 mL ascorbic acid solution, mix well, add 2 mL molybdate solution, mix well, let stand for 15 min, and measure the absorbance at 700 nm with a UV spectrophotometer. Check the phosphate content from the working curve. The phosphate removal rate is the ratio of the phosphate removal before and after the experiment to the phosphate content of the original water sample.

[0058] III. Analysis of test results of various embodiments and comparative examples Take the water samples at 0 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, and 10 h in the experimental groups of Example 1, Example 2, and Comparative Example 1, and filter them through a 0.22 μm polyethersulfone filter membrane. Test the concentrations of ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and phosphate in the water samples, calculate the removal rates of ammonia nitrogen, inorganic nitrogen (including ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen), and phosphate, and draw the removal rate graphs of ammonia nitrogen, inorganic nitrogen, and phosphate in the experimental groups of Example 1, Example 2, and Comparative Example 1, as shown in FIG. Figure 1 and Figure 2 shown.

[0059] from Figure 1 and Figure 2 It can be seen that the algae-bacteria ratio of 1:1 experimental group has a better effect on the removal of ammonia nitrogen and inorganic nitrogen. The ammonia nitrogen removal rates of the algae-bacteria ratio of 0:1, algae-bacteria ratio of 0.5:1, and algae-bacteria ratio of 1:1 are 50%, 54%, and 57% at 10 h, respectively, and the inorganic nitrogen removal rates are 53%, 57%, and 61%, respectively. The removal rates of ammonia nitrogen and inorganic nitrogen are ranked from large to small as follows: algae-bacteria ratio of 1:1>algae-bacteria ratio of 0.5:1>algae-bacteria ratio of 0:1, indicating that increasing the inoculation ratio of the algae ball is beneficial to the removal of ammonia nitrogen and inorganic nitrogen.

[0060] from Figure 1 and Figure 2 It can be seen that the phosphate removal rates of the experimental groups with an algae-bacteria ratio of 0.5:1 and 1:1 at 10 h were 10%, 80% and 90%, respectively, indicating that the phosphate removal rate was the highest under the algae-bacteria ratio of 1:1, which was much higher than the phosphate removal rates under the algae-bacteria ratio of 0:1 and 0.5:1. Increasing the inoculation ratio of the algae ball is beneficial to the removal of phosphate. Within the time range of 5 to 10 h, the phosphate removal rate increased rapidly, which was closely related to the addition of sodium acetate in the 5th hour, providing sodium acetate as an organic carbon source to the algae-bacteria symbiotic system, promoting the absorption and utilization of phosphate.

[0061] The algae balls used to treat sewage in Example 1 were taken and the morphology of the algae balls after use was tested. Figure 3 and Figure 4 .from Figure 3 and Figure 4 It can be seen that the surface of the algae ball after use is rough and the overall shape is round. There are many gaps on the surface of the algae ball, which provide the transfer of reaction substrates. Some algae cells are attached to the surface of the algae ball, and some algae cells are embedded in the algae ball.

[0062] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing an immobilized algae ball, characterized in that: The steps include: S1. Take a culture solution of Chlorella in the logarithmic growth phase, centrifuge to obtain concentrated Chlorella, mix the concentrated Chlorella with deionized water to obtain an algae solution, prepare a sodium alginate solution, and mix the algae solution and the sodium alginate solution evenly to obtain a mixed solution; S2. Prepare CaCl2 solution, slowly add the mixed solution into the CaCl2 solution, fix and cross-link for 23 to 25 hours at room temperature, and obtain algae balls after washing with deionized water.

2. The method for preparing immobilized algae balls according to claim 1, characterized in that: The concentration of the algae solution in step S1 is 8.5-9.5 g / L.

3. The method for preparing immobilized algae balls according to claim 1, characterized in that: The concentration of the sodium alginate solution in step S1 is 40 g / L.

4. The method for preparing immobilized algae balls according to claim 1, characterized in that: In step S1, the algae solution and the sodium alginate solution are mixed evenly in a volume ratio of 1:(2-3).

5. The method for preparing immobilized algae balls according to claim 1, characterized in that: The concentration of the CaCl2 solution in step S2 is 20 g / L.

6. An immobilized algae ball, characterized in that: The immobilized algae ball is prepared by the preparation method of the immobilized algae ball according to any one of claims 1 to 5.

7. An immobilized algae ball and bacteria symbiotic system, characterized in that: A mixed solution comprising the algae balls and activated sludge as described in claim 6.

8. The immobilized algae ball and bacteria symbiotic system according to claim 7, characterized in that: The activated sludge is short-range nitrification sludge, and the concentration of the activated sludge is 1.0 g / L.

9. The immobilized algae ball and bacteria symbiotic system according to claim 7, characterized in that: The mass ratio of the activated sludge to the algae balls is 1:(0.5~1).

10. The use of an immobilized algae ball and bacteria symbiotic system in sewage treatment according to any one of claims 7 to 9, characterized in that: The method comprises the following steps: adding algae balls and activated sludge mixture into sewage, aerating the sewage for 5 hours under light conditions, with an aeration flow rate of 0.9-1.0 L / min; adding an organic carbon source to the sewage and stopping aeration at the 5th hour of reaction, and continuing the reaction for 5 hours; performing microfiltration after the reaction is completed, and the sewage treatment is completed.

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