Method for preparing a membrane for selective removal of phosphates from wastewater and use of the membrane

Abstract

The application discloses a preparation method of a membrane for selectively removing phosphates in wastewater and application of the membrane, and the membrane is a PVC / Zr-BT membrane, and the preparation method comprises the following steps: (1) Zr-BT preparation: natural bentonite is added into a ZrOCl2 solution, uniformly stirred, then a NaOH solution is added to adjust pH, and continuously stirred to obtain a precipitate, the precipitate is filtered, dried, ground and sieved to obtain Zr-BT; (2) PVC / Zr-BT membrane: Zr-BT and PVC are sequentially added into NMP, uniformly stirred, then the solution is subjected to ultrasonic and vacuum degassing treatment, then an appropriate amount of casting solution is poured on an automatic film casting machine, the membrane is obtained after being immersed in water after film casting. The PVC / Zr-BT membrane has the advantages of simple preparation method, high removal efficiency of phosphates in wastewater, and can be used as a single phosphorus source of microalgae, and has the dual functions of wastewater purification and resource recycling.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a membrane and application of the membrane, in particular to a membrane for selectively removing phosphates and application of the membrane in aquaculture wastewater treatment and microalgae cultivation, and belongs to the field of membrane adsorption separation and wastewater treatment. BACKGROUND

[0002] In recent years, marine aquaculture has become increasingly intensive, and the problems that follow have also become more and more. Excessive discharge of seawater aquaculture wastewater containing nutrients (nitrogen, phosphorus) into seawater will lead to eutrophication and reduced dissolved oxygen, and is harmful to marine organisms, thereby further endangering human health. Eutrophication is mainly caused by nitrogen and phosphorus, but phosphorus cannot be fixed from the atmosphere like nitrogen, so phosphorus is considered to be the main cause and limiting factor of eutrophication.

[0003] Phosphorus is also an important non-renewable resource, and according to the current trend, it may be depleted in 50-100 years. A review shows that eutrophic seawater may become phosphate rock in the future, so a sustainable phosphorus recovery strategy should be applied to the marine system to control eutrophication while providing phosphorus for the growing market demand.

[0004] In the existing related patents of PVC membranes, the main contents include the hydrophilicity and hydrophobicity (application number: CN202010975161.8), anti-pollution performance (application number: CN201710480968.2) and the like, and there is no research on selective adsorption of phosphates, so it is of great significance to use the PVC / Zr-BT membrane to treat wastewater and selectively adsorb phosphates in the wastewater and for microalgae cultivation for the first time, and to recycle and reuse the phosphorus resource. SUMMARY

[0005] The purpose of the application is to provide a preparation method of a membrane for selectively removing phosphates in wastewater, the membrane prepared by the method has excellent phosphate selective adsorption effect and removal capacity in addition to improved water flux of the PVC membrane, and the mechanical strength is also improved; another purpose of the application is to provide a method for removing phosphates in aquaculture wastewater by using the above-mentioned membrane; and another purpose of the application is to provide a method for cultivating microalgae by using the above-mentioned membrane.

[0006] Technical scheme: The application provides a preparation method of a membrane for selectively removing phosphates in wastewater, the membrane is a PVC / Zr-BT membrane, and the preparation method comprises the following steps:

[0007] (1) Preparation of Zr-BT: natural bentonite is added into a ZrOCl2 solution, uniformly stirred, then a NaOH solution is added to adjust the pH, and continues to be stirred to obtain a precipitate, and the precipitate is filtered, dried, ground and sieved to obtain the Zr-BT;

[0008] (2) PVC / Zr-BT film: Zr-BT and PVC were added into NMP in turn, stirred uniformly, then the solution was treated by ultrasonic and vacuum degassing, after that, an appropriate amount of casting solution was poured on the automatic film casting machine, after film casting, it was put into water for soaking, and the PVC / Zr-BT film was obtained.

[0009] Further, in step (1), the mass ratio of natural bentonite to ZrOCl2 solution is 1:10-20. The mass fraction of ZrOCl2 solution is 2%. The mass ratio of natural bentonite to ZrOCl2 in ZrOCl2 solution is 10:1-2.

[0010] Further, in step (1), the pH is adjusted to 8-9.

[0011] Further, in step (1), the stirring time of natural bentonite after adding ZrOCl2 solution is 2-4 h, the stirring time of adding NaOH solution is 2-3 h, and the drying time is 12-24 h.

[0012] Further, in step (2), the mass of Zr-BT, PVC and NMP is 5-20:10:70-85.

[0013] Further, in step (2), the stirring time of Zr-BT and PVC after adding into NMP is 2-4 h, the ultrasonic time is 0.5-1 h, the vacuum degassing time is 0.5-2 h, and the soaking time is 24-48 h.

[0014] On the other hand, the present application provides a method for removing phosphate in aquaculture wastewater, which comprises the following steps:

[0015] On the other hand, the present application provides a method for culturing microalgae, which comprises the following steps:

[0016] (1) placing the PVC / Zr-BT film in the aquaculture wastewater to adsorb the phosphate in the aquaculture wastewater, and obtaining the PVC / Zr-BT film adsorbed with the phosphate;

[0017] (2) adding the PVC / Zr-BT film adsorbed with the phosphate into the microalgae culture medium to culture the microalgae.

[0018] Further, in step (2), the light intensity for culturing the microalgae is 100-200 mol photons / (m-2.s-1), and the temperature is 20-25℃.

[0019] Further, in step (2), the PVC / Zr-BT membrane with adsorbed phosphate is subjected to phosphorus desorption or directly added into the microalgae culture medium without phosphorus desorption.

[0020] The present application will be described in detail by Zr 4+ The natural bentonite is modified to obtain Zr-BT powder which can effectively adsorb phosphate, and the Zr 4+ The selectivity for phosphate is improved. However, the powdered adsorbent is not easy to separate from water, and if it is used to remove phosphate in water, secondary pollution will be caused. By fixing the Zr-BT adsorbent in the membrane, the above problems are solved, and the combination of the Zr-BT adsorbent and the membrane brings unexpected effects to the membrane, improving the water flux and mechanical properties of the PVC membrane, and the selectivity of the Zr-BT adsorbent for phosphate and the removal capacity are also improved.

[0021] Advantages: Compared with the prior art, the present application has the following obvious advantages: (1) filling the blank of PVC membrane in the study of phosphate adsorption, and reasonably utilizing the phosphorus resources adsorbed by the membrane; (2) using natural and low-cost BT to fill the PVC membrane, greatly increasing the water flux and the phosphate removal effect of the membrane; (3) the prepared membrane has good adsorption and desorption properties, and the mechanical strength is increased to enable repeated use. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The scanning electron micrograph of the PVC membrane;

[0023] Figure 2 The scanning electron micrograph of the PVC / BT membrane;

[0024] Figure 3 The scanning electron micrograph of the PVC / Zr-BT membrane;

[0025] Figure 4 The changes of algal cell density in M1, M2, M3 and M4 culture media in Example 8;

[0026] Figure 5 The changes of chlorophyll a content in M1, M2, M3 and M4 culture media in Example 8. DETAILED DESCRIPTION

[0027] The present application will be described in detail by Zr

[0028] Example 1

[0029] (1) Preparation of Zr-BT: 10 g of natural bentonite was added to a beaker containing 100 mL of 2% ZrOCl2solution, stirred at 500 rpm on a magnetic stirrer for 3 h, then 1 mol / L NaOH solution was added to adjust the pH to 8.0 and continue to stir for 2 h, then pure water was added for washing, and after centrifugation at 5000 rpm on a high-speed centrifuge for 3 times, it was placed in an oven and dried at 60°C for 24 h. After complete drying, it was ground through a 200 mesh sieve to obtain Zr-BT.

[0030] (2) Preparation of PVC / Zr-BT membrane: 5 g of Zr-BT and 10 g of PVC were sequentially added to a beaker containing 85 g of NMP, stirred at 500 rpm on a magnetic stirrer for 4 h, and after uniform stirring, the beaker containing the casting solution was placed in an ultrasonic cleaner for ultrasonic treatment for 1 h, then placed in a vacuum oven and vacuum degassed at 60°C for 0.5 h. After treatment, an appropriate amount of casting solution was poured on an automatic film casting machine, and the film thickness was adjusted to 200 μm by adjusting the film casting machine. After casting, it was immersed in pure water for 24 h to completely replace the organic solvent and water. After film formation, it was cut into a rectangle with an area of 70 cm 2 .

[0031] (3) Cross-sectional SEM image of PVC / Zr-BT membrane, the results are shown in Figure 3 : The SEM image of the film side can see the granular Zr-BT, which shows that the adsorbent is successfully loaded inside the membrane, and the "finger-like" structure on the surface of the membrane is reduced, and the layered structure inside the membrane is increased.

[0032] (4) Membrane performance test: the PVC / Zr-BT membrane prepared in step (2) was placed on a triple high-pressure flat membrane test device for phosphate adsorption experiment. The initial concentration of phosphate solution used for adsorption experiment was 1 mg / L, the volume was 3 L, and the phosphate concentration after adsorption was measured after 24 h. The phosphate removal rate was calculated; the water flux of the membrane was calculated by collecting the water flowing through the membrane in 5 min using a conical flask.

[0033] Example 2

[0034] (1) Preparation of Zr-BT: 10 g of natural bentonite was added to a beaker containing 100 mL of 2% ZrOCl2solution, stirred at 500 rpm on a magnetic stirrer for 3 h, then 1 mol / L NaOH solution was added to adjust the pH to 8.0 and continue to stir for 2 h, then pure water was added for washing, and after centrifugation at 5000 rpm on a high-speed centrifuge for 3 times, it was placed in an oven and dried at 60°C for 24 h. After complete drying, it was ground through a 200 mesh sieve to obtain Zr-BT.

[0035] (2) Preparation of PVC / Zr-BT membrane: 10 g of Zr-BT and 10 g of PVC were sequentially added to a beaker containing 80 g of NMP, stirred on a magnetic stirrer at 500 rpm for 4 h, and then placed in an ultrasonic cleaner for 1 h after uniform stirring. Then, the beaker containing the casting solution was placed in a vacuum oven, degassed at 60°C for 0.5 h, and then an appropriate amount of casting solution was poured onto an automatic film casting machine. The film thickness was adjusted to 200 pm, and then the film was immersed in pure water for 24 h to completely replace the organic solvent and water. After film formation, the film was cut into a rectangle with an area of 70 cm 2 .

[0036] (3) Membrane performance test: The PVC / Zr-BT membrane prepared in step (2) was placed on a triple high-pressure flat membrane test device for phosphate adsorption experiment. The initial concentration of the phosphate solution used for the adsorption experiment was 1 mg / L, and the volume was 3 L. After 24 h, the phosphate concentration after adsorption was measured, and the phosphate removal rate was calculated. The water flux of the membrane was calculated by collecting the water flowing through the membrane in 5 min using a conical flask.

[0037] Example 3

[0038] (1) Preparation of Zr-BT: 10 g of natural bentonite was added to a beaker containing 100 mL of 2% ZrOCl2 solution, stirred on a magnetic stirrer at 500 rpm for 3 h, and then 1 mol / L NaOH solution was added to adjust the pH to 8.0. After stirring for 2 h, the solution was washed with pure water and centrifuged at 5000 rpm for 3 times. Then, the solution was placed in an oven and dried at 60°C for 24 h. After complete drying, the solution was ground through a 200 mesh sieve to obtain Zr-BT.

[0039] (2) Preparation of PVC / Zr-BT membrane: 15 g of Zr-BT and 10 g of PVC were sequentially added to a beaker containing 75 g of NMP, stirred on a magnetic stirrer at 500 rpm for 4 h, and then placed in an ultrasonic cleaner for 1 h after uniform stirring. Then, the beaker containing the casting solution was placed in a vacuum oven, degassed at 60°C for 0.5 h, and then an appropriate amount of casting solution was poured onto an automatic film casting machine. The film thickness was adjusted to 200 pm, and then the film was immersed in pure water for 24 h to completely replace the organic solvent and water. After film formation, the film was cut into a rectangle with an area of 70 cm 2 .

[0040] (3) Membrane performance test: The PVC / Zr-BT membrane prepared in step (2) was placed on a triple high-pressure flat membrane test device for phosphate adsorption experiment. The initial concentration of the phosphate solution used for the adsorption experiment was 1 mg / L, and the volume was 3 L. After 24 h, the phosphate concentration after adsorption was measured, and the phosphate removal rate was calculated. The water flux of the membrane was calculated by collecting the water flowing through the membrane in 5 min using a conical flask.

[0041] Example 4

[0042] (1) Preparation of Zr-BT: 10 g of natural bentonite was added to a beaker containing 100 mL of a 2% by mass ZrOCl2solution, stirred at 500 rpm on a magnetic stirrer for 3 h, then 1 mol / L NaOH solution was added to adjust the pH to 8.0 and continue to stir for 2 h, then pure water was added for washing, centrifuged at 5000 rpm on a high-speed centrifuge for 3 times, and then placed in an oven for drying at 60°C for 24 h. After complete drying, it was ground through a 200 mesh sieve to obtain Zr-BT.

[0043] (2) Preparation of PVC / Zr-BT membrane: 20 g of Zr-BT and 10 g of PVC were sequentially added to a beaker containing 70 g of NMP, stirred at 500 rpm on a magnetic stirrer for 4 h, then the beaker containing the casting solution was placed in an ultrasonic cleaner for ultrasonic treatment for 1 h, then placed in a vacuum oven for vacuum degassing at 60°C for 0.5 h, then an appropriate amount of casting solution was poured on an automatic film casting machine, the film thickness was adjusted to 200 μm, and after casting, it was immersed in pure water for 24 h to completely replace the organic solvent and water. After film formation, it was cut into a rectangle with an area of 70 cm 2 .

[0044] (3) Membrane performance test: The PVC / Zr-BT membrane prepared in step (2) was placed on a triple high-pressure flat membrane test device for phosphate adsorption experiment. The initial concentration of the phosphate solution used for the adsorption experiment was 1 mg / L, the volume was 3 L, and the phosphate concentration after adsorption was measured after 24 h. The phosphate removal rate was calculated; the water flux of the membrane was calculated by collecting the water flowing through the membrane in 5 min using a conical flask.

[0045] Example 5

[0046] (1) Preparation of Zr-BT: 10 g of natural bentonite was added to a beaker containing 100 mL of a 2% by mass ZrOCl2solution, stirred at 500 rpm on a magnetic stirrer for 3 h, then 1 mol / L NaOH solution was added to adjust the pH to 8.0 and continue to stir for 2 h, then pure water was added for washing, centrifuged at 5000 rpm on a high-speed centrifuge for 3 times, and then placed in an oven for drying at 60°C for 24 h. After complete drying, it was ground through a 200 mesh sieve to obtain Zr-BT.

[0047] (2) Preparation of PVC / Zr-BT membrane: 10 g of Zr-BT and 10 g of PVC were sequentially added to a beaker containing 80 g of NMP, stirred on a magnetic stirrer at 500 rpm for 4 h, and then placed in an ultrasonic cleaner for 1 h after uniform stirring. Then, the beaker containing the casting solution was placed in a vacuum oven, degassed at 60°C for 0.5 h, and then an appropriate amount of casting solution was poured onto an automatic film coater, and the film thickness was adjusted to 100 pm. After casting, the film was immersed in pure water for 24 h to completely replace the organic solvent and water. After film formation, the film was cut into a rectangle with an area of 70 cm 2 .

[0048] (3) Membrane performance test: The PVC / Zr-BT membrane prepared in step (2) was placed on a triple high-pressure flat membrane test device for phosphate adsorption experiment. The initial concentration of the phosphate solution used for the adsorption experiment was 1 mg / L, and the volume was 3 L. After 24 h, the phosphate concentration after adsorption was measured, and the phosphate removal rate was calculated. The water flux of the membrane was calculated by collecting the water flowing through the membrane in 5 min using a conical flask.

[0049] Example 6

[0050] (1) Preparation of Zr-BT: 10 g of natural bentonite was added to a beaker containing 100 mL of 2% ZrOCl2 solution, stirred on a magnetic stirrer at 500 rpm for 3 h, and then 1 mol / L NaOH solution was added to adjust the pH to 8.0, and then stirred for 2 h. Then, the solution was washed with pure water and centrifuged at 5000 rpm for 3 times. Then, the solution was placed in an oven and dried at 60°C for 24 h. After complete drying, the solution was ground through a 200 mesh sieve to obtain Zr-BT.

[0051] (2) Preparation of PVC / Zr-BT membrane: 10 g of Zr-BT and 10 g of PVC were sequentially added to a beaker containing 80 g of NMP, stirred on a magnetic stirrer at 500 rpm for 4 h, and then placed in an ultrasonic cleaner for 1 h after uniform stirring. Then, the beaker containing the casting solution was placed in a vacuum oven, degassed at 60°C for 0.5 h, and then an appropriate amount of casting solution was poured onto an automatic film coater, and the film thickness was adjusted to 300 pm. After casting, the film was immersed in pure water for 24 h to completely replace the organic solvent and water. After film formation, the film was cut into a rectangle with an area of 70 cm 2 .

[0052] (3) Membrane performance test: The PVC / Zr-BT membrane prepared in step (2) was placed on a triple high-pressure flat membrane test device for phosphate adsorption experiment. The initial concentration of the phosphate solution used for the adsorption experiment was 1 mg / L, and the volume was 3 L. After 24 h, the phosphate concentration after adsorption was measured, and the phosphate removal rate was calculated. The water flux of the membrane was calculated by collecting the water flowing through the membrane in 5 min using a conical flask.

[0053] Example 7

[0054] (1) Preparation of Zr-BT: 10 g of natural bentonite was added to a beaker containing 100 mL of a 2% by mass ZrOCl2solution, stirred at 500 rpm on a magnetic stirrer for 3 h, then 1 mol / L NaOH solution was added to adjust the pH to 8.0 and continue to stir for 2 h, then pure water was added for washing, centrifuged at 5000 rpm on a high-speed centrifuge for 3 times, and then placed in an oven for drying at 60°C for 24 h. After complete drying, it was ground through a 200 mesh sieve to obtain Zr-BT.

[0055] (2) Preparation of PVC / Zr-BT membrane: 10 g of Zr-BT and 10 g of PVC were sequentially added to a beaker containing 80 g of NMP, stirred at 500 rpm on a magnetic stirrer for 4 h, then the beaker containing the casting solution was placed in an ultrasonic cleaner for ultrasonic treatment for 1 h, then placed in a vacuum oven for vacuum degassing at 60°C for 0.5 h, then an appropriate amount of casting solution was poured on an automatic film casting machine, the film thickness was adjusted to 500 μm, and after casting, it was immersed in pure water for 24 h to completely replace the organic solvent and water. After film formation, it was cut into a rectangle with an area of 70 cm 2

[0056] (3) Membrane performance test: the PVC / Zr-BT membrane prepared in step (2) was placed on a triple high-pressure flat membrane test device for phosphate adsorption experiment. The initial concentration of the phosphate solution used for the adsorption experiment was 1 mg / L, the volume was 3 L, and the phosphate concentration after adsorption was measured after 24 h. The phosphate removal rate was calculated; the water flux of the membrane was calculated by collecting the water flowing through the membrane in 5 min using a conical flask.

[0057] Example 8

[0058] (1) Preparation of Zr-BT: 10 g of natural bentonite was added to a beaker containing 100 mL of a 2% by mass ZrOCl2solution, stirred at 500 rpm on a magnetic stirrer for 3 h, then 1 mol / L NaOH solution was added to adjust the pH to 8.0 and continue to stir for 2 h, then pure water was added for washing, centrifuged at 5000 rpm on a high-speed centrifuge for 3 times, and then placed in an oven for drying at 60°C for 24 h. After complete drying, it was ground through a 200 mesh sieve to obtain Zr-BT.

[0059] ​(2) Preparation of PVC / Zr-BT membrane: 10 g of Zr-BT and 10 g of PVC were added into a beaker containing 80 g of NMP, and stirred on a magnetic stirrer at 500 rpm for 4 h. After uniform stirring, the beaker containing the casting solution was placed in an ultrasonic cleaner for ultrasonic treatment for 1 h, and then placed in a vacuum oven for vacuum degassing at 60 °C for 0.5 h. After that, an appropriate amount of casting solution was poured on an automatic film casting machine, and the film thickness was adjusted to 200 pm by adjusting the casting knife. After casting, it was immersed in pure water for 24 h to completely replace the organic solvent and water. After film formation, it was cut into a rectangle with an area of 70 cm 2 .

[0060] (3) Removal of phosphate in aquaculture wastewater: The PVC / Zr-BT membrane prepared in step (2) was placed on a triple high-pressure flat membrane test device for phosphate adsorption experiments. Sea cucumber aquaculture wastewater with a TP concentration of 0.448 mg / L was used for the adsorption experiment, with a volume of 3 L. After 24 h, the phosphate concentration after adsorption was measured, and the phosphate removal rate was calculated.

[0061] (4) Cultivation of Phaeodactylum tricornutum: The PVC / Zr-BT membrane adsorbed with phosphate in step (3) was collected and used as a phosphorus source in M3 or M4 medium. Equal amounts of Phaeodactylum tricornutum algal liquid were inoculated into four types of media: M1 (sea cucumber wastewater), M2 (f / 2), M3 (phosphorus-free f / 2 + membrane adsorbed and desorbed phosphorus), and M4 (phosphorus-free f / 2 + membrane adsorbed phosphorus). The four types of media were sterilized at 121 °C for 15 min. The M3 medium was prepared by immersing the membrane adsorbed with phosphate in 1 mol / L NaOH for 3 h to desorb the phosphorus. The M4 medium was prepared by directly adding the membrane adsorbed with phosphate into the phosphorus-free f / 2 medium.

[0062] In each medium, the initial algal liquid concentration was 1 x 10 5 cells / mL, and the culture was carried out in a light incubator with a light intensity of 100 pm photons / (m -2 .s -1 ), a temperature of 20 °C, and a light incubation time of 16 days. The change in algal cell density and the final chlorophyll content were recorded. As shown in Figure 4 , it can be seen that the PVC / Zr-BT membrane adsorbed with phosphate added to the phosphorus-free f / 2 medium has similar growth conditions to the f / 2 medium. In the M1 medium, the microalgae began to decrease in concentration after 4 days due to the lack of sufficient nutrients. In the M2 and M4 media, both had comparable maximum cell concentrations (9 x 10 6 cells / mL), indicating that the phosphorus source on the PVC / Zr-BT membrane can gradually elute into the medium as the microalgae consume it, thereby meeting the microalgae's demand for phosphorus.

[0063] Figure 5 The difference of microalgae chlorophyll a content in four kinds of medium was shown. In M1 medium, the lack of nutrients affected the photosynthesis of microalgae, and the synthesis of chlorophyll was inhibited; the chlorophyll a content in M2 and M3 was equivalent, while the chlorophyll a content in M4 medium was 1.2 times of that in M2, which might be attributed to the elution of phosphorus on PVC / Zr-BT over time.

[0064] Example 9

[0065] Compared with Example 1, the difference was that in the preparation of Zr-BT in step (1), the mass fraction of ZrOCl2 solution was 1%, the mass ratio of natural bentonite to ZrOCl2 solution was 1:20; the pH was adjusted to 9; the stirring time of natural bentonite after adding ZrOCl2 solution was 2-4h, the stirring time after adding NaOH solution was 2-3h, and the drying time was 12-24h; in the preparation of PVC / Zr-BT membrane in step (2), the stirring time of Zr-BT and PVC after adding to NMP was 2-4h, the ultrasonic time was 0.5-1h, and the vacuum degassing time was 0.5-2h; the soaking time was 24-48h.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 2 was that no Zr-BT was added, and the obtained membrane was a pure PVC membrane. Subsequently, the membrane water flux and phosphate adsorption capacity test were carried out.

[0068] The SEM of the cross section of the PVC membrane is shown in Figure 1 It is obvious that the cross section of the pure PVC membrane is smooth, no granular substance loading is observed, and the membrane surface has a "finger-like" structure, which is due to the characteristics of the membrane prepared by phase inversion method.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 2 was that unmodified BT was added, and the obtained was a BT-filled mixed matrix PVC membrane. Subsequently, the membrane water flux and phosphate adsorption capacity test were carried out.

[0071] The SEM of the cross section of the PVC / BT membrane is shown in Figure 2 The cross section of the PVC / BT membrane has similar characteristics to the PVC / Zr-BT membrane.

[0072] Table 1 is a performance comparison of the mixed matrix membranes prepared in Examples 1-7 and Comparative Examples 1-2. It can be seen that the PVC / Zr-BT membranes prepared by the present preparation method can improve the water flux and phosphate removal rate of the mixed matrix membranes. The introduction of Zr-BT increases the pore size and surface roughness of the membranes, which is the main reason for the improvement of water flux. The present application optimizes the preparation of PVC / Zr-BT membranes, and the optimal parameters are: 10% Zr-BT content in the casting solution, and a membrane thickness of 200 μm.

[0073] Table 1 is a performance comparison of the reverse osmosis membrane elements prepared in Examples 1-4 and Comparative Examples

[0074] Reverse osmosis membrane Water flux (L m -2 ·h -1 ) ]]> PO4 3- Removal (%)]]> Example 1 820 70.4 Example 2 940 98.5 Example 3 597 83.2 Example 4 269 86.5 Example 5 1053 56.6 Example 6 167 83.1 Example 7 57 63.5 Comparative Example 1 315 7.5 Comparative Example 2 956 30.5

[0075] Table 2 shows the changes in parameters before and after the treatment of sea cucumber aquaculture wastewater in Example 8

[0076]

[0077]

[0078] The above is only the preferred embodiment of the present application, and it should be noted that for those skilled in the art, without departing from the inventive concept, several modifications and improvements can be made, which all belong to the protection scope of the present application.

[0079] It should be understood that for those skilled in the art, modifications or changes can be made according to the above description, and all these modifications and changes shall belong to the protection scope of the appended claims of the present application.

Claims

1. A method for preparing a membrane for selectively removing phosphates from wastewater, characterized in that, The membrane is a PVC / Zr-BT membrane, and its preparation method includes the following steps: (1) Preparation of Zr-BT: Natural bentonite was added to ZrOCl2 solution and stirred evenly. Then NaOH solution was added to adjust the pH and stirring was continued to obtain a precipitate. After filtration, drying, grinding and sieving, Zr-BT was obtained. The mass ratio of natural bentonite to ZrOCl2 in ZrOCl2 solution was 10:1~2. (2) PVC / Zr-BT membrane: Zr-BT and PVC are added to NMP in sequence and stirred evenly. Then the solution is subjected to ultrasonic and vacuum degassing treatment. After that, an appropriate amount of casting liquid is poured on an automatic film coating machine, and the film is coated and immersed in water to form a PVC / Zr-BT membrane. The mass ratio of Zr-BT, PVC and NMP is 5:10:85, 10:10:80 or 15:10:

75.

2. The method for preparing a membrane for selectively removing phosphates from wastewater according to claim 1, characterized in that, In step (1), adjust the pH to 8-9.

3. The method for preparing a membrane for selectively removing phosphates from wastewater according to claim 1, characterized in that, In step (1), the stirring time after adding ZrOCl2 solution to natural bentonite is 2-4 h, and the stirring time after adding NaOH solution is 2-3 h. The drying time is 12-24 h.

4. The method for preparing a membrane for selectively removing phosphates from wastewater according to claim 1, characterized in that, In step (2), the stirring time after adding Zr-BT and PVC to NMP is 2~4 h, the ultrasonic time is 0.5~1 h, the vacuum degassing time is 0.5~2 h, and the soaking time is 24~48 h.

5. A method for removing phosphates from aquaculture wastewater, characterized in that, The PVC / Zr-BT membrane prepared by the method described in claim 1 is placed in the aquaculture wastewater to be treated to adsorb phosphates in the aquaculture wastewater. After the adsorption is completed, the PVC / Zr-BT membrane is removed to complete the phosphate removal.

6. A method for cultivating microalgae, characterized in that, Includes the following steps: (1) The PVC / Zr-BT membrane prepared by the method of claim 1 is placed in aquaculture wastewater to adsorb phosphate in the aquaculture wastewater, thereby obtaining a PVC / Zr-BT membrane adsorbed with phosphate. (2) Add the PVC / Zr-BT membrane with phosphate adsorbed to the microalgae culture medium for microalgae cultivation.

7. The microalgae cultivation method according to claim 6, characterized in that, In step (2), the microalgae cultivation environment is characterized by a light intensity of 100~200 mol photons / (m²). -2 . s -1 The temperature is 20~25℃.

8. The microalgae cultivation method according to claim 6, characterized in that, In step (2), the PVC / Zr-BT membrane adsorbed with phosphate is either desorbed or added directly to the microalgae culture medium without desorption.

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