A method for treating wastewater from marine aquaculture

Abstract

This invention provides a method for treating effluent from marine aquaculture, comprising the following steps: Step 1: The effluent is precipitated using a composite flocculant and then filtered to obtain pretreated seawater; Step 2: The pretreated seawater is discharged into a composite microalgae culture tank for secondary purification for 6-8 days, and then filtered through a nanofiltration membrane; wherein, the composite flocculant comprises the following raw materials in parts by weight: diatomaceous earth 30-45 parts, fly ash 20-35 parts, polyaluminum chloride 35-45 parts, *Gynostemma pentaphyllum* extract 18-25 parts, *Polygonum hydropiper* extract 20-30 parts, *Polygonum hydropiper* extract 18-30 parts, sodium alginate 20-35 parts, modified β-cyclodextrin 16-26 parts, and nanocellulose 14-22 parts. This invention utilizes a composite flocculant, composite microalgae, and a filtration membrane to treat aquaculture wastewater, effectively reducing the pollutant content in the wastewater, improving the discharge standards of marine aquaculture wastewater, and achieving good treatment results.

Description

Technical Field

[0001] This invention relates to the field of aquaculture water purification technology, and in particular to a method for treating marine aquaculture wastewater. Background Technology

[0002] Marine aquaculture is a production method that artificially cultivates animals or marine plants in tidal flats, shallow seas, and other marine areas using methods such as flow-through aquaculture, pond aquaculture, and cage aquaculture. It is currently an important aquaculture method in my country. The aquaculture process consumes a large amount of water resources, resulting in wastewater. If this wastewater is not properly treated, it will generate a large amount of pollutants, causing serious pollution and burden on the environment. The main sources of pollutants in marine aquaculture wastewater are animal feces, feed, chemicals, and fish mucus. Currently, fish are mainly fed synthetic feed, and only a small amount of nitrogen and phosphorus compounds in these feeds can be absorbed and utilized by fish; the rest are essentially pollutants that accumulate in the marine aquaculture wastewater. In recent years, due to the continuous expansion of the aquaculture industry, seawater pollution has become increasingly serious. Current methods for treating marine aquaculture wastewater mainly include physical, chemical, biological, and ecological methods, as well as a combination of these methods. However, the treatment process still faces problems such as the generation of toxic and harmful substances, complexity, low efficiency, and poor treatment results. Summary of the Invention

[0003] In view of this, the present invention proposes a method for treating wastewater from marine aquaculture.

[0004] The technical solution of this invention is implemented as follows:

[0005] A method for treating wastewater from marine aquaculture includes the following steps:

[0006] Step 1: After the wastewater is settled by a composite flocculant, it is filtered to obtain pretreated seawater;

[0007] Step 2: After the pretreated seawater is discharged into the composite microalgae culture tank for secondary purification treatment for 6-8 days, it can be filtered through a nanofiltration membrane.

[0008] The composite flocculant comprises the following raw materials in parts by weight: 30-45 parts diatomaceous earth, 20-35 parts fly ash, 35-45 parts polyaluminum chloride, 18-25 parts alligator lily extract, 20-30 parts physalis extract, 18-30 parts Polygonum hydropiper extract, 20-35 parts sodium alginate, 16-26 parts modified β-cyclodextrin, and 14-22 parts nanocellulose.

[0009] Furthermore, the dosage of the composite flocculant is 120–140 mg / L; the nanofiltration membrane is a ceramic filtration membrane with a pore size of 100 nm–1000 nm.

[0010] Furthermore, the composite microalgae culture tank cultivates composite microalgae, including Chlorella, Spirulina, and Scenedesmus; the culture cell density of the composite microalgae is 1.0–4.0 × 10⁻⁶ cells / year. 5 Cells / mL; the ratio of cultured cells of Chlorella, Spirulina and Scenedesmus is 6-8:3-6:1.

[0011] Furthermore, the preparation method of the composite flocculant is as follows:

[0012] (I): Diatomaceous earth and fly ash were respectively subjected to high-temperature calcination to obtain pretreated powder;

[0013] (II): Add the extracts of alligator crocodile flower, lantern grass, and Polygonum hydropiper to water and stir to prepare a mixed extract solution; add sodium alginate to water and stir to obtain a sodium alginate solution; stir and mix the mixed extract solution, sodium alginate solution, and nanocellulose to obtain a pretreated mixture;

[0014] (III): Add the pretreated mixture obtained in (II) above to the pretreated powder obtained in (I) above, stir and mix well, then perform high-pressure impregnation treatment, then add polyaluminum chloride, modified β-cyclodextrin and nanocellulose, stir and mix well, dry, and pulverize to obtain the composite flocculant.

[0015] Furthermore, in the above (a), the high-temperature calcination temperature is 800-1200℃ and the time is 60-120min.

[0016] Furthermore, in (ii) above, the mass concentration of the mixed extract solution is 60-80%; and the mass concentration of the sodium alginate solution is 10-15%.

[0017] Furthermore, in the above (ii), the stirring speed is 400-700 r / min, the temperature is 30-60℃, and the time is 15-30 min.

[0018] Furthermore, in the above (iii), the pressure of the high-pressure impregnation is 15-40 MPa and the time is 60-90 min.

[0019] Furthermore, the preparation method of the modified β-cyclodextrin is as follows: beet pectin solution is added to carboxymethyl-β-cyclodextrin solution and mixed evenly, then glutaraldehyde solution with a mass concentration of 20-30% is slowly added dropwise, the mixture is stirred and reacted at 60-75℃ for 60-90 minutes, filtered, the filter cake is washed with distilled water 3-5 times until neutral, and then dried and pulverized to obtain modified β-cyclodextrin.

[0020] Furthermore, the mass ratio of carboxymethyl-β-cyclodextrin to beet pectin is 3-5:1; the preparation process of the carboxymethyl-β-cyclodextrin solution is as follows: carboxymethyl-β-cyclodextrin is added to distilled water to prepare a carboxymethyl-β-cyclodextrin solution with a mass concentration of 20-30%; the preparation process of the beet pectin solution is as follows: beet pectin is added to distilled water and stirred evenly to prepare a beet pectin solution with a mass concentration of 10-15%.

[0021] Furthermore, the neutrality of the polyaluminum chloride is n = 1 to 5.

[0022] Furthermore, the preparation method of the alligator beak flower extract is as follows: after crushing the alligator beak flower, add 8 to 10 times the weight of water to mix and decoct, then filter. Add 3 to 5 times the weight of water to the filter residue and decoct again. Repeat 2 to 3 times, combine the filtrates, and concentrate to a water content of 50 to 60% to obtain the alligator beak flower extract.

[0023] Furthermore, the preparation method of the *Lysimachia christinae* extract is as follows: after crushing *Lysimachia christinae*, add 6 to 8 times the weight of water to mix, then boil and filter. Add 3 to 4 times the weight of water to the filter residue and boil again. Repeat this process 2 to 3 times, then combine the filtrates and concentrate to a water content of 50 to 60% to obtain *Lysimachia christinae* extract.

[0024] Furthermore, the preparation method of the Polygonum hydropiper extract is as follows: after crushing Polygonum hydropiper, add 6 to 8 times the weight of water to mix and decoct, then filter. Add 3 to 4 times the weight of water to the filter residue and decoct again. Repeat 2 to 3 times, combine the filtrates, and concentrate to a water content of 50 to 60% to obtain the Polygonum hydropiper extract.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. This invention utilizes composite flocculants, composite microalgae, and filter membranes to treat aquaculture wastewater, effectively reducing pollutant content and improving discharge standards for marine aquaculture wastewater, demonstrating excellent treatment results. During the treatment process, the composite flocculant first adsorbs and precipitates pollutants such as animal feces, aquaculture feed, and ammonia nitrogen in the wastewater. Simultaneously, the flocculant sterilizes the wastewater, enhancing purification efficiency. The pretreated seawater, after treatment with the composite flocculant, is then discharged into an aquaculture pond containing composite microalgae for secondary purification. The composite microalgae further purify residual ammonia nitrogen, phosphorus, and other nutrients in the wastewater, further improving purification. Furthermore, the cultivated composite microalgae are rich in protein, carbohydrates, vitamins, and other substances. These algae can be further processed into animal feed and bait, improving resource utilization and reducing purification costs.

[0027] 2. In the preparation process of the composite flocculant of the present invention, the high-temperature calcination of diatomaceous earth and fly ash can improve the porosity and structural stability of the pores. In the subsequent high-pressure impregnation process with extracts of alligator lily, calcinus grass, Polygonum hydropiper, and sodium alginate, the retention rate of active substances such as extracts of alligator lily in diatomaceous earth and fly ash can be effectively improved, thereby promoting the adsorption performance and bactericidal effect in the subsequent wastewater treatment process and improving the treatment efficiency.

[0028] 3. In the process of preparing modified β-cyclodextrin, beet pectin is cross-linked with carboxymethyl-β-cyclodextrin to improve the stability of β-cyclodextrin, enhance its adsorption effect, and also play a certain bactericidal role. Detailed Implementation

[0029] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0030] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0031] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0032] The Chlorella sp., Spirulina sp., and Scenedesmus sp. in the composite microalgae of this invention are derived from Shanghai Guangyu Biotechnology Co., Ltd.

[0033] Example 1

[0034] The composite flocculant of this embodiment includes the following raw materials in parts by weight: 40 parts diatomaceous earth, 25 parts fly ash, 42 parts polyaluminum chloride, 20 parts alligator lily extract, 25 parts physalis extract, 22 parts Polygonum hydropiper extract, 30 parts sodium alginate, 18 parts modified β-cyclodextrin, and 16 parts nanocellulose.

[0035] The preparation method of this composite flocculant is as follows:

[0036] (I): Diatomaceous earth and fly ash were calcined at 1100℃ for 100 min to obtain pretreated powder.

[0037] (II): Add the extracts of alligator crocodile flower, lantern grass, and Polygonum hydropiper to water and stir to prepare a mixed extract solution with a mass concentration of 70%; add sodium alginate to water and stir to obtain a sodium alginate solution with a mass concentration of 12%; stir and mix the mixed extract solution, sodium alginate solution, and nanocellulose to obtain a pretreated mixture.

[0038] (III): Add the pretreated mixture obtained in (II) above to the pretreated powder obtained in (I) above and stir and mix for 25 min at a speed of 500 r / min and a temperature of 40℃. Then, perform high-pressure impregnation treatment at a pressure of 25 MPa for 70 min. Then, add polyaluminum chloride, modified β-cyclodextrin and nanocellulose and stir and mix for 20 min at a speed of 500 r / min and a temperature of 50℃. Dry and pulverize to obtain the composite flocculant.

[0039] The method for treating marine aquaculture wastewater in this embodiment includes the following steps:

[0040] Step 1: After the effluent is precipitated by a composite flocculant, it is filtered to obtain pretreated seawater; the dosage of the composite flocculant is 140 mg / L.

[0041] Step Two: After the pretreated seawater is discharged into the culture tank for the cultivation of composite microalgae for secondary purification for 7 days, it is then filtered through a nano-ceramic filter membrane with a pore size of 100nm to 1000nm; the cultured cell density of the composite microalgae is 2.0 × 10⁻⁶ cells / year. 5 The composite microalgae consist of Chlorella, Spirulina, and Scenedesmus with a colony density ratio of 6:4:1.

[0042] Example 2

[0043] The composite flocculant of this embodiment includes the following raw materials in parts by weight: 30-45 parts diatomaceous earth, 20-35 parts fly ash, 35-45 parts polyaluminum chloride, 18-25 parts alligator lily extract, 20-30 parts physalis extract, 18-30 parts Polygonum hydropiper extract, 20-35 parts sodium alginate, 16-26 parts modified β-cyclodextrin, and 14-22 parts nanocellulose;

[0044] The preparation method of this composite flocculant is as follows:

[0045] (I): Diatomaceous earth and fly ash were calcined at 1200℃ for 120 min to obtain pretreated powder.

[0046] (II): Add the extracts of alligator crocodile flower, lantern grass, and Polygonum hydropiper to water and stir to prepare a mixed extract solution with a mass concentration of 80%; add sodium alginate to water and stir to obtain a sodium alginate solution with a mass concentration of 15%; stir and mix the mixed extract solution, sodium alginate solution, and nanocellulose to obtain a pretreated mixture.

[0047] (III): Add the pretreated mixture obtained in (II) above to the pretreated powder obtained in (I) above and stir and mix for 30 min at a speed of 700 r / min and a temperature of 60℃. Then, perform high-pressure impregnation treatment at a pressure of 40 MPa for 90 min. Then, add polyaluminum chloride, modified β-cyclodextrin and nanocellulose and stir and mix for 30 min at a speed of 700 r / min and a temperature of 60℃. Dry and pulverize to obtain the composite flocculant.

[0048] The method for treating marine aquaculture wastewater in this embodiment includes the following steps:

[0049] Step 1: After the effluent is precipitated by a composite flocculant, it is filtered to obtain pretreated seawater; the dosage of the composite flocculant is 140 mg / L.

[0050] Step Two: After 8 days of secondary purification treatment, the pretreated seawater is discharged into the culture tank for cultivating composite microalgae. Then, it is filtered through a nano-ceramic filter membrane with a pore size of 100nm–1000nm. The cell density of the composite microalgae is 1.0 × 10⁻⁶ cells / year. 5 The composite microalgae consists of Chlorella, Spirulina and Scenedesmus with a cultured cell density ratio of 8:6:1.

[0051] Example 3

[0052] The composite flocculant of this embodiment includes the following raw materials in parts by weight: 30 parts diatomaceous earth, 20 parts fly ash, 35 parts polyaluminum chloride, 18 parts alligator lily extract, 20 parts physalis extract, 18 parts Polygonum hydropiper extract, 20 parts sodium alginate, 16 parts modified β-cyclodextrin, and 14 parts nanocellulose.

[0053] The preparation method of this composite flocculant is as follows:

[0054] (I): Diatomaceous earth and fly ash were calcined at 800℃ for 60 minutes to obtain pretreated powder.

[0055] (II): Add the extracts of alligator crocodile flower, lantern grass, and Polygonum hydropiper to water and stir to prepare a mixed extract solution with a mass concentration of 60%; add sodium alginate to water and stir to obtain a sodium alginate solution with a mass concentration of 10%; stir and mix the mixed extract solution, sodium alginate solution, and nanocellulose to obtain a pretreated mixture.

[0056] (III): Add the pretreated mixture obtained in (II) above to the pretreated powder obtained in (I) above and stir and mix for 15 min at a speed of 400 r / min and a temperature of 30℃. Then, perform high-pressure impregnation treatment at a pressure of 15 MPa for 60 min. Then, add polyaluminum chloride, modified β-cyclodextrin and nanocellulose and stir and mix for 15 min at a speed of 400 r / min and a temperature of 30℃. Dry and pulverize to obtain the composite flocculant.

[0057] The method for treating marine aquaculture wastewater in this embodiment includes the following steps:

[0058] Step 1: After the effluent is settled by passing it through a composite flocculant, it is filtered to obtain pretreated seawater; the dosage of the composite flocculant is 130 mg / L.

[0059] Step Two: After the pretreated seawater is discharged into the culture tank for the cultivation of composite microalgae for secondary purification for 6 days, it is then filtered through a nano-ceramic filter membrane with a pore size of 100nm to 1000nm; the cultured cell density of the composite microalgae is 3.0 × 10⁻⁶ cells / year. 5 The composite microalgae consists of Chlorella, Spirulina and Scenedesmus with a cultured cell density ratio of 6:3:1.

[0060] The modified β-cyclodextrin is prepared as follows: Carboxymethyl-β-cyclodextrin and beet pectin are taken at a mass ratio of 4:1. Carboxymethyl-β-cyclodextrin is added to distilled water to prepare a 25% carboxymethyl-β-cyclodextrin solution. Beet pectin is added to distilled water and stirred evenly to prepare a 12% beet pectin solution. The beet pectin solution is added to the carboxymethyl-β-cyclodextrin solution and mixed evenly. Then, a 26% glutaraldehyde solution is slowly added dropwise. The mixture is stirred and reacted at 70°C for 80 minutes and then filtered. The filter cake is washed four times with distilled water until neutral. After drying and pulverizing, the modified β-cyclodextrin is obtained.

[0061] Example 4

[0062] The composite flocculant of this embodiment includes the following raw materials in parts by weight: 32 parts diatomaceous earth, 30 parts fly ash, 38 parts polyaluminum chloride, 22 parts alligator lily extract, 28 parts physalis extract, 26 parts Polygonum hydropiper extract, 25 parts sodium alginate, 24 parts modified β-cyclodextrin, and 20 parts nanocellulose.

[0063] The preparation method of this composite flocculant is as follows:

[0064] (I): Diatomaceous earth and fly ash were calcined at 1000℃ for 90 minutes to obtain pretreated powder.

[0065] (II): Add the extracts of alligator crocodile flower, lantern grass, and Polygonum hydropiper to water and stir to prepare a mixed extract solution with a mass concentration of 65%; add sodium alginate to water and stir to obtain a sodium alginate solution with a mass concentration of 14%; stir and mix the mixed extract solution, sodium alginate solution, and nanocellulose to obtain a pretreated mixture.

[0066] (III): Add the pretreated mixture obtained in (II) above to the pretreated powder obtained in (I) above and stir and mix for 20 min at a speed of 600 r / min and a temperature of 50℃. Then, perform high-pressure impregnation treatment at a pressure of 30 MPa for 80 min. Then, add polyaluminum chloride, modified β-cyclodextrin and nanocellulose and stir and mix for 25 min at a speed of 450 r / min and a temperature of 40℃. Dry and pulverize to obtain the composite flocculant.

[0067] The method for treating marine aquaculture wastewater in this embodiment includes the following steps:

[0068] Step 1: After the effluent is precipitated by a composite flocculant, it is filtered to obtain pretreated seawater; the dosage of the composite flocculant is 120 mg / L.

[0069] Step Two: After the pretreated seawater is discharged into the culture tank for the cultivation of composite microalgae for secondary purification for 7 days, it is then filtered through a nano-ceramic filter membrane with a pore size of 100nm to 1000nm; the cultured cell density of the composite microalgae is 4.0 × 10⁻⁶ cells / year. 5 The composite microalgae consists of Chlorella, Spirulina and Scenedesmus with a colony density ratio of 7:5:1.

[0070] The modified β-cyclodextrin is prepared as follows: Carboxymethyl-β-cyclodextrin and beet pectin are taken at a mass ratio of 3:1. Carboxymethyl-β-cyclodextrin is added to distilled water to prepare a carboxymethyl-β-cyclodextrin solution with a mass concentration of 28%. Beet pectin is added to distilled water and stirred evenly to prepare a beet pectin solution with a mass concentration of 14%. The beet pectin solution is added to the carboxymethyl-β-cyclodextrin solution and mixed evenly. Then, a glutaraldehyde solution with a mass concentration of 22% is slowly added dropwise. The mixture is stirred and reacted at 65°C for 70 minutes and then filtered. The filter cake is washed 5 times with distilled water until neutral. After drying and pulverizing, the modified β-cyclodextrin is obtained.

[0071] Comparative Example 1

[0072] The difference between this comparative example and Example 1 is that the preparation method of the composite flocculant is different.

[0073] The composite flocculant of this comparative example includes the following raw materials in parts by weight: 40 parts diatomaceous earth, 25 parts fly ash, 42 parts polyaluminum chloride, 20 parts alligator lily extract, 25 parts physalis extract, 22 parts Polygonum hydropiper extract, 30 parts sodium alginate, 18 parts modified β-cyclodextrin, and 16 parts nanocellulose.

[0074] The preparation method of the composite flocculant is as follows: diatomaceous earth, fly ash, polyaluminum chloride, sodium alginate, modified β-cyclodextrin, nanocellulose, alligator lily extract, lantern grass extract, and Polygonum hydropiper extract are stirred and mixed for 20 minutes at a speed of 500 r / min and a temperature of 50℃, then dried and pulverized to obtain the composite flocculant.

[0075] The treatment method for marine aquaculture wastewater in this comparative example includes the following steps:

[0076] Step 1: After the effluent is precipitated by a composite flocculant, it is filtered to obtain pretreated seawater; the dosage of the composite flocculant is 140 mg / L.

[0077] Step Two: After the pretreated seawater is discharged into the culture tank for the cultivation of composite microalgae for secondary purification for 7 days, it is then filtered through a nano-ceramic filter membrane with a pore size of 100nm to 1000nm; the cultured cell density of the composite microalgae is 2.0 × 10⁻⁶ cells / year. 5The composite microalgae consist of Chlorella, Spirulina, and Scenedesmus with a colony density ratio of 6:4:1.

[0078] Comparative Example 2

[0079] The difference between this comparative example and Example 1 is that the composite flocculant contains only 40 parts of diatomaceous earth and 42 parts of polyaluminum chloride.

[0080] The treatment method for marine aquaculture wastewater in this comparative example includes the following steps:

[0081] Step 1: After the effluent is precipitated by a composite flocculant, it is filtered to obtain pretreated seawater; the dosage of the composite flocculant is 140 mg / L.

[0082] Step 2: After the pretreated seawater is discharged into the culture tank for secondary purification for 7 days, it can be filtered through a nano-ceramic filter membrane with a pore size of 100nm to 1000nm. The culture density of the composite microalgae is 0.3g / L, and the composite microalgae consists of Chlorella, Spirulina and Scenedesmus in a mass ratio of 6:4:1.

[0083] Comparative Example 3

[0084] The difference between this comparative example and Example 1 is that the process of using a flocculant is missing.

[0085] The treatment method for seawater aquaculture wastewater in this comparative example involves the following steps: Pretreated seawater is discharged into a culture tank containing composite microalgae for secondary purification for 7 days, followed by filtration through a nano-ceramic filter membrane with a pore size of 100nm–1000nm; the cell density of the composite microalgae is 2.0 × 10⁻⁶ cells / year. 5 The composite microalgae consist of Chlorella, Spirulina, and Scenedesmus with a colony density ratio of 6:4:1.

[0086] The wastewater from marine aquaculture was treated using the methods of Examples 1-4 and Comparative Examples 1-3 of this invention, and the content of corresponding indicators in the wastewater before and after treatment was measured, and the corresponding removal rate was calculated.

[0087] Removal rate (%) = (M0-M1) / M0×100%, where M0 is the content of total nitrogen, total phosphorus, ammonia nitrogen and suspended solids in the original marine aquaculture wastewater, and M1 is the content of total nitrogen, total phosphorus, ammonia nitrogen and suspended solids in the treated wastewater.

[0088] Total nitrogen was determined using alkaline potassium persulfate digestion ultraviolet spectrophotometry, ammonia nitrogen using Nessler's reagent spectrophotometry, and total phosphorus using potassium persulfate digestion molybdate spectrophotometry. Suspended solids were determined using a gravimetric method. The antibacterial efficiency was calculated as (S0 - S1) / S0 × 100%, where S0 and S1 represent the residual bacterial counts after bacterial culture of the wastewater before and after treatment, respectively.

[0089] The wastewater treatment test results are shown in Table 1 below.

[0090]

[0091]

[0092] The above results show that the treatment method of the present invention in Examples 1-4 can effectively purify wastewater generated from marine aquaculture, especially with the combined effect of the flocculant and composite microalgae of the present invention. In contrast, the wastewater treated in Comparative Examples 1-3, which did not use the flocculant of the present invention or was prepared using flocculants prepared by different methods, showed poorer effects in removing pollutants and sterilizing Escherichia coli, Staphylococcus aureus, etc. The method of the present invention can effectively improve treatment efficiency and also has a sterilizing effect during the treatment process.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating wastewater from marine aquaculture, characterized in that, Includes the following steps: Step 1: After the wastewater is settled by a composite flocculant, it is filtered to obtain pretreated seawater; Step Two: After the pretreated seawater is discharged into the composite microalgae cultivation tank for secondary purification for 6-8 days, it is then filtered through a nanofiltration membrane. The composite microalgae cultivation tank cultivates composite microalgae, including Chlorella, Spirulina, and Scenedesmus. The cell density of the composite microalgae is 1.0~4.0 × 10⁻⁶ cells / year. 5 Cells / mL; the ratio of cultured cells of Chlorella, Spirulina and Scenedesmus is 6~8:3~6:1; The composite flocculant comprises the following raw materials in parts by weight: 30-45 parts diatomaceous earth, 20-35 parts fly ash, 35-45 parts polyaluminum chloride, 18-25 parts alligator lily extract, 20-30 parts physalis extract, 18-30 parts Polygonum hydropiper extract, 20-35 parts sodium alginate, 16-26 parts modified β-cyclodextrin, and 14-22 parts nanocellulose; The preparation method of the composite flocculant is as follows: (a): Diatomaceous earth and fly ash are respectively subjected to high-temperature calcination to obtain pretreated powder; (ii): Add the extracts of alligator crocodile flower, lantern grass, and Polygonum hydropiper to water and stir to prepare a mixed extract solution; add sodium alginate to water and stir to obtain a sodium alginate solution; stir and mix the mixed extract solution, sodium alginate solution, and nanocellulose to obtain a pretreated mixture; (iii): Add the pretreated mixture obtained in (ii) above to the pretreated powder obtained in (i) above, stir and mix well, then perform high-pressure impregnation treatment, then add polyaluminum chloride, modified β-cyclodextrin and nanocellulose, stir and mix well, dry, and pulverize to obtain the composite flocculant.

2. The method for treating marine aquaculture wastewater according to claim 1, characterized in that, The dosage of the composite flocculant is 120~140mg / L; the nanofiltration membrane is a ceramic filtration membrane with a pore size of 100nm~1000nm.

3. The method for treating marine aquaculture wastewater according to claim 1, characterized in that, In the above (a), the high-temperature calcination temperature is 800~1200℃ and the time is 60~120min.

4. The method for treating marine aquaculture wastewater according to claim 1, characterized in that, In (ii) above, the mass concentration of the mixed extract solution is 60-80%; the mass concentration of the sodium alginate solution is 10-15%.

5. The method for treating marine aquaculture wastewater according to claim 1, characterized in that, In step (ii) above, the stirring speed is 400~700 r / min, the temperature is 30~60℃, and the time is 15~30 min.

6. The method for treating marine aquaculture wastewater according to claim 1, characterized in that, In the above (iii), the pressure of the high-pressure impregnation is 15~40MPa and the time is 60~90min.

7. The method for treating marine aquaculture wastewater according to claim 1, characterized in that, The modified β-cyclodextrin is prepared by adding beet pectin solution to carboxymethyl-β-cyclodextrin solution and mixing evenly, then slowly adding glutaraldehyde solution with a mass concentration of 20-30%, stirring and reacting at 60-75℃ for 60-90 minutes, filtering, washing the filter cake with distilled water 3-5 times until neutral, and then drying and pulverizing to obtain modified β-cyclodextrin.

8. The method for treating marine aquaculture wastewater according to claim 7, characterized in that, The mass ratio of carboxymethyl-β-cyclodextrin to beet pectin is 3~5:1; the preparation process of the carboxymethyl-β-cyclodextrin solution is as follows: carboxymethyl-β-cyclodextrin is added to distilled water to prepare a carboxymethyl-β-cyclodextrin solution with a mass concentration of 20~30%; the preparation process of the beet pectin solution is as follows: beet pectin is added to distilled water and stirred evenly to prepare a beet pectin solution with a mass concentration of 10~15%.

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