A method and application for directional diatom cultivation using aquaculture wastewater

Abstract

The application discloses a method for directional culture of diatoms by using aquaculture tail water and application, and belongs to the cross field of aquaculture and wastewater treatment. The method for directional culture of diatoms by using aquaculture tail water comprises the following steps: S1, precipitation: discharging the aquaculture tail water into a sedimentation tank to make silt and large particles precipitate; S2, sterilization and algae removal: sterilizing and removing original algae in the aquaculture tail water by irradiating the aquaculture tail water with ultraviolet rays; S3, nutrition structure adjustment: adjusting total salinity of the aquaculture tail water to be 20-30 ‰, adjusting silicate content to be 500-1000 micromoles / L, adjusting phosphate content to be 0.6-0.9 mg / L, and adjusting ammonium salt content to be 4-6 mg / L; and S4, inoculation of algal species and bacteria and culture: inoculating diatoms and diatom symbiotic bacteria into the aquaculture tail water. By using the method, directional regulation of a microalgal community in the aquaculture tail water can be realized, and the removal rate of nutrient salts in the aquaculture tail water and the resource recovery rate can be greatly improved. Meanwhile, byproduct shellfishes can be cultured and put on the market, economic benefits can be improved, and purification cost can be reduced.

Description

Technical Field

[0001] This invention relates to the intersection of aquaculture and wastewater treatment, and more specifically, to a method and application for the directional cultivation of diatoms using aquaculture wastewater. Background Technology

[0002] In order to achieve high yields and profits in mariculture, large amounts of feed are often required. The unused feed and animal excrement degrade in the water, leading to increased nitrogen and phosphorus levels. Currently, my country restricts the discharge of mariculture wastewater, requiring it to be treated before discharge. Unlike industrial wastewater, mariculture wastewater is not toxic, making resource recovery during treatment crucial. Currently, a combination of microalgae and shellfish filter feeding is a commonly used model for wastewater treatment and resource recovery. This model utilizes microalgae to absorb nutrients from the wastewater, while economically important marine shellfish such as razor clams and hard clams filter-feed to absorb particulate matter, thus achieving nitrogen and phosphorus purification and resource recovery. However, in current wastewater treatment applications, the nutrient structure in most wastewater is unsuitable for diatom growth. Currently, microalgae growth areas in wastewater treatment facilities lack nutrient regulation and are only equipped with aeration facilities. Aeration alone is insufficient for algal growth, and nutrient absorption is inadequate. Even after subsequent filter feeding by shellfish, inorganic salt levels remain excessive, necessitating additional treatment processes, which are time-consuming and labor-intensive. Furthermore, the algae and bacteria in the aquaculture effluent are highly complex, and directly adding diatomaceous earth often yields poor results. Added algae rarely become dominant species, and competition for nutrients and ecological niches between bacteria and algae can easily lead to the collapse of the microalgal community. Summary of the Invention

[0003] The problem this invention aims to solve is how to improve the survival rate and biomass of diatoms in aquaculture wastewater.

[0004] To address the above problems, this invention provides an ecological purification method for aquaculture wastewater, comprising the following steps:

[0005] S1. Sedimentation: The aquaculture wastewater is discharged into the sedimentation tank to allow silt and large particles to settle.

[0006] S2. Sterilization and algae removal: Using ultraviolet light with a wavelength of 254nm to irradiate the aquaculture wastewater to kill bacteria and existing algae in the wastewater.

[0007] S3. Nutrient Structure Adjustment: Adjusting the salt content in the aquaculture wastewater. The parameters for adjusting the salt content in the aquaculture wastewater include total salinity, silicate content, phosphate content, and ammonium content. The total salinity is 20-30‰, the silicate content is 500-1000 μmol / L, the phosphate content is 0.6-0.9 mg / L, and the ammonium content is 4-6 mg / L.

[0008] S4. Inoculation and cultivation of algae and bacteria: Inoculate diatoms and diatom symbiotic bacteria into the aquaculture tailwater, and cultivate for 3-7 days under a light intensity of not less than 4000 lux and a light duration of not less than 12 hours / day.

[0009] Compared to traditional aquaculture wastewater treatment, the purification method provided by this invention adds a sterilization and algae removal step. In this step, most of the indigenous algae and microorganisms in the wastewater are killed by ultraviolet light. This lays the foundation for diatoms and diatom symbiotic bacteria to gain an advantage and acquire ecological niches in the subsequent competition between diatoms and indigenous algae, and between diatom symbiotic bacteria and indigenous bacteria. Simultaneously, ultraviolet irradiation of the wastewater can convert some organic matter into absorbable nutrients. This invention also adds a nutrient structure adjustment step, in which the total salt content and the ratio of various salts are optimized to achieve a balanced nutrient structure in the wastewater.

[0010] Preferably, in step S4, the diatom species is selected from any one or more of Chaetoceros muelleri, Leymus chinensis, Rhombus crepusca, and Cyclostrum spp.

[0011] Preferably, in step S4, the diatom implantation density is determined by the following parameter: the concentration of diatom chlorophyll in the diatoms in the aquaculture tailwater is 300-500 μg / L.

[0012] Preferably, in step S4, the diatom symbiotic bacteria are selected from any one or more of Marinobacter sp., Alteromonas macleodii, and Muricauda sp.

[0013] Preferably, in step S4, the planting density of the diatom symbiotic bacteria is 10. 4 ~10 6 cell / mL.

[0014] Preferably, in step S1, the precipitation time is greater than or equal to 24 hours.

[0015] Furthermore, a second aspect of the present invention provides an application of the aforementioned method for directional cultivation of diatoms using aquaculture wastewater, wherein the application involves co-culturing diatoms with shellfish to use diatoms as feed for shellfish.

[0016] Preferably, when using shellfish culture ponds for polyculture, the height of the shellfish culture ponds shall not be less than 20cm.

[0017] Preferably, the density of the shellfish in the aquaculture tailwater is 50,000 to 200,000 shellfish / m³. 2 .

[0018] Preferably, the shellfish is selected from one or more of the following: razor clam, mud clam, blue clam, Manila clam, and hard clam.

[0019] Existing aquaculture wastewater treatment facilities have the following drawbacks:

[0020] 1. The nutrient structure in aquaculture wastewater is unbalanced, making it unsuitable for diatom growth in most cases. Currently, the microalgae growth zone in aquaculture wastewater treatment lacks nutrient regulation and is only equipped with aeration facilities. Aeration alone cannot meet the needs of algae growth, and nutrient absorption is insufficient. Even after subsequent filter feeding by shellfish, inorganic salt levels remain excessive, requiring additional treatment processes, which are time-consuming and labor-intensive.

[0021] 2. The algae and bacteria in aquaculture wastewater are highly complex, and directly adding diatomaceous earth is often ineffective. Added algae rarely become dominant species, and competition for nutrients and niches between bacteria and algae can easily lead to the collapse of the microalgal community. When aquaculture wastewater is centrally treated, it comes from various ponds and factories. Some algae in this wastewater may not be suitable for shellfish digestion and absorption, such as cyanobacteria and dinoflagellates. Furthermore, aquaculture wastewater also contains pathogens, which are harmful to the shellfish being treated.

[0022] The beneficial effects of this invention are as follows: The aquaculture wastewater purification method provided by this invention regulates the nutrient salts and microorganisms (algae and bacteria) in the wastewater, including a series of processes such as sterilization and algae elimination, nutrient regulation, inoculation with exogenous high-efficiency algae strains, and regulation with diatom symbiotic bacteria, to promote the targeted cultivation of diatoms in the wastewater. Addressing defect 1, this invention utilizes a nutrient salt regulation scheme to control silicate, phosphate, nitrogen, and salinity to achieve the optimal nutritional state for diatoms, while allowing diatoms to utilize these nitrogen and phosphorus nutrients after 3-7 days of growth. Addressing defect 2, this invention uses UV sterilization to reduce the influence of existing bacteria and microalgae, and then adds exogenous diatom strains and diatom symbiotic bacteria to ensure the dominant growth of diatoms. After regulation using the method of this invention, the proportion of diatoms in the aquaculture wastewater will be over 90%, and the diatom biomass will increase by 5-10 times. Combined with the shellfish filter-feeding treatment process in the wastewater, this will greatly improve the nutrient removal rate and resource recovery rate of the wastewater.

[0023] Furthermore, in the ecological purification method for aquaculture wastewater provided by this invention, the final product, in addition to aquaculture wastewater that meets the discharge standards, also includes shellfish organisms. These shellfish organisms can eventually be cultured again into adult shellfish for market, which is beneficial to improving the economic benefits of aquaculture. Attached Figure Description

[0024] Figure 1 This is a graph showing the growth trend of diatom chlorophyll content in the experimental group and the control group when the wastewater from factory farming was used as aquaculture wastewater in Example 1 of the present invention.

[0025] Figure 2 This is a graph showing the growth trend of chlorophyll content in green algae in the experimental group and the control group when the wastewater from factory farming was used as aquaculture wastewater in Example 1 of the present invention.

[0026] Figure 3 This is a graph showing the growth trend of diatom chlorophyll content in the experimental group and the control group when the wastewater from the earthen pond is used as aquaculture wastewater in a specific embodiment of the present invention.

[0027] Figure 4 This is a graph showing the growth trend of diatom chlorophyll content in the experimental group and the control group when the wastewater from the earthen pond is used as aquaculture wastewater in a specific embodiment of the present invention.

[0028] Figure 5 This is a graph showing the growth trend of diatom chlorophyll content in the experimental group and the control group when the mixed wastewater from industrial wastewater and earthen pond wastewater is used as aquaculture wastewater in a specific embodiment of the present invention.

[0029] Figure 6 This is a graph showing the growth trend of diatom chlorophyll content in the experimental group and the control group when the mixed wastewater from industrial wastewater and earthen pond wastewater is used as aquaculture wastewater in a specific embodiment of the present invention.

[0030] Figure 7 This is a flowchart of an ecological purification method for aquaculture wastewater provided in a specific embodiment of the present invention. Detailed Implementation

[0031] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0032] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] Example 1

[0034] In this embodiment, the wastewater from shrimp factory farming was used as the aquaculture wastewater. The original salinity of the wastewater was measured to be 22‰, the silicate content was 132 μmol / L, the phosphate content was 0.2 mg / L, the ammonium nitrogen content was 3.1 mg / L, the nitrite content was 0.5 mg / L, the nitrate content was 2.2 mg / L, the diatom chlorophyll content was 170 μg / L, and the green algae chlorophyll content was 421 μg / L.

[0035] S1: The aquaculture wastewater was discharged into a sedimentation tank through a ditch and allowed to settle for 24 hours before being divided into a control group and an experimental group.

[0036] S2: The control group's aquaculture wastewater was left untreated. The experimental group's wastewater was transferred to a sterilization and algae removal tank equipped with five 350W ultraviolet lamps (254nm wavelength). The wastewater was irradiated with ultraviolet lamps for 10 minutes. After treatment, the chlorophyll content of diatoms in the experimental group's wastewater was 68 μg / L, and that of green algae was 102 μg / L. In the control group, the untreated chlorophyll content of diatoms was 150 μg / L, and that of green algae was 330 μg / L.

[0037] S3: Adjust the silicate concentration in the aquaculture wastewater of the experimental group and the control group after step S2 to 500 μmol / L, the phosphate concentration to 0.9 mg / L, and the ammonium concentration to 6 mg / L. The nutrient adjustment is now complete.

[0038] S4: After completing step S3, add Chaetoceros algae solution to the control group and experimental group to control the final diatom chlorophyll content to 500 μg / L. Add diatom symbiotic bacteria solution of Marinobacter sp., Alteronas macleodii, and Muricauda sp., with the concentration controlled at 10. 4 Cell / mL. After inoculation, the chlorophyll content of diatoms, the chlorophyll content of green algae, and the nitrogen and phosphorus salt content in the culture effluent were measured daily. The test results are as follows: Figure 1 and Figure 2 As shown, the diatom concentration in the aquaculture effluent consistently increased over 7 days, rising from 170 μg / L to 2500 μg / L after 7 days. In the UV-treated group, green algae remained at low levels, and nitrogen and phosphorus levels in the effluent both decreased to below 0.01 mg / L. The control group also underwent nutrient regulation and the addition of diatoms and bacteria, but did not receive UV irradiation treatment. In this control group, green algae concentration consistently increased, reaching 1100 μg / L, while diatom concentration remained at low levels.

[0039] Green algae cannot be consumed by shellfish, and the diatom content in the control group was too low. Therefore, the control group could not be used for the experiment of shellfish consuming diatoms.

[0040] S5: Construct shellfish farming ponds with dimensions of 4*3*0.5 meters (length*width*height). Add 55,000 shellfish per m³ to the ponds. 2 After the razor clams are removed, the culture wastewater containing diatoms, which has been treated in step S4, is added. It is determined that the culture wastewater rich in diatoms is used in the razor clam and shellfish surface flow tank. The diatoms are completely utilized after the wastewater stays in the shellfish culture tank for 1 hour.

[0041] Example 2

[0042] In this embodiment, the tailwater from an earthen pond was used as the aquaculture tailwater. The original salinity of the aquaculture tailwater was measured to be 23‰, the silicate content was 85 μmol / L, the phosphate content was 0.32 mg / L, the ammonium nitrogen content was 0.85 mg / L, the nitrite content was 0.3 mg / L, the nitrate content was 2.0 mg / L, the diatom chlorophyll content was 89 μg / L, and the green algae chlorophyll content was 35 μg / L.

[0043] S1: The aquaculture wastewater was discharged into a sedimentation tank through a ditch and allowed to settle for 24 hours before being divided into a control group and an experimental group.

[0044] S2: The control group's aquaculture wastewater was left untreated. The experimental group's wastewater was transferred to a sterilization and algae removal tank equipped with five 350W ultraviolet lamps (254nm wavelength). The wastewater was irradiated with ultraviolet lamps for 10 minutes. After treatment, the chlorophyll content of diatoms in the experimental group's wastewater was 19 μg / L, and that of green algae was 18 μg / L. In the control group, the untreated chlorophyll content of diatoms was 93 μg / L, and that of green algae was 30 μg / L.

[0045] S3: Adjust the silicate concentration in the aquaculture wastewater of the experimental group and the control group after step S2 to 500 μmol / L, the phosphate concentration to 0.6 mg / L, and the ammonium concentration to 4 mg / L. The nutrient adjustment is now complete.

[0046] S4: After completing step S3, add Chaetoceros algae solution to the control group and experimental group to control the final diatom chlorophyll content to 323 μg / L. Add diatom symbiotic bacteria solution of Marinobacter sp., Alteromonas macleodii, and Muricauda sp., with the concentration controlled at 2 × 10⁻⁶. 5 Cell / mL. After inoculation, the chlorophyll content of diatoms, the chlorophyll content of green algae, and the nitrogen and phosphorus salt content in the culture effluent were measured daily. The test results are as follows: Figure 3 and Figure 4 As shown, the diatom concentration in the aquaculture effluent consistently increased over 7 days, reaching 2348 μg / L after 7 days. In the UV-treated group, green algae remained at a low level, and nitrogen and phosphorus levels in the effluent both decreased to below 0.01 mg / L. The control group also underwent nutrient regulation and the addition of diatoms and bacteria, but did not receive UV irradiation treatment. After 2 days of growth, the diatom concentration rose to around 830 μg / L before starting to decline, eventually dropping to around 300 μg / L, while green algae remained at a low level.

[0047] Green algae have low feed value and the diatom content in the control group is too low. Therefore, the control group cannot be used to conduct experiments on shellfish consuming diatoms.

[0048] S5: Construct shellfish farming ponds with dimensions of 4*3*0.5 meters (length*width*height). Add 150,000 shellfish per m³ to the ponds.2 After the mud clams are added, the diatom-containing aquaculture wastewater from step S4 is added. It is determined that the diatom-rich aquaculture wastewater is utilized in the mud clam shellfish surface flow tank. The diatoms are completely utilized after the wastewater stays in the shellfish aquaculture tank for 1 hour.

[0049] Example 3

[0050] In this embodiment, a mixture of industrial wastewater and pond wastewater is used as aquaculture wastewater. This aquaculture wastewater is also mixed with some natural precipitation due to rainwater. The original salinity of the aquaculture wastewater is 15‰, silicate is 53μmol / L, phosphate is 0.28mg / L, ammonium nitrogen is 1.1mg / L, nitrite is 0.48mg / L, nitrate is 1.9mg / L, diatom chlorophyll is 90μg / L, and cyanobacterial chlorophyll is 20μg / L.

[0051] S1: The aquaculture wastewater was discharged into a sedimentation tank through a ditch and allowed to settle for 24 hours before being divided into a control group and an experimental group.

[0052] S2: The control group's aquaculture wastewater was left untreated. The experimental group's wastewater was transferred to a sterilization and algae removal tank equipped with five 350W ultraviolet lamps (254nm wavelength). The wastewater was irradiated with ultraviolet lamps for 10 minutes. After treatment, the experimental group's wastewater contained 22 μg / L of diatom chlorophyll and 0 μg / L of cyanobacteria chlorophyll. In the control group, the untreated wastewater contained 60 μg / L of diatom chlorophyll and 5.7 μg / L of cyanobacteria chlorophyll.

[0053] S3: Adjust the total salinity of the aquaculture tailwater of the experimental group and the control group after step S2 to 22‰, the silicate to 1000μmol / L, the phosphate to 0.8mg / L, and the ammonium to 5mg / L. The nutrient adjustment is complete.

[0054] S4: After completing step S3, add Chaetoceros algae solution to the control group and experimental group to control the final diatom chlorophyll content to 470 μg / L. Add diatom symbiotic bacteria solution of Marinobacter sp., Alteronas macleodii, and Muricauda sp., with the concentration controlled at 10. 6 After planting, the chlorophyll content of diatoms and cyanobacteria, as well as the nitrogen and phosphorus salt content in the aquaculture effluent were measured daily. The test results are as follows: Figure 5 and Figure 6As shown, diatoms in the aquaculture effluent showed an increasing trend over 7 days, reaching 3016 μg / L after 7 days. In the UV-treated group, cyanobacteria levels remained low, and nitrogen and phosphorus levels in the effluent both decreased to below 0.01 mg / L. The control group also underwent nutrient regulation and the addition of diatoms and bacteria, but did not receive UV irradiation treatment. Diatoms reached 1500 μg / L after the third day and then began to decline, reaching only around 400 μg / L on the seventh day, while cyanobacteria levels remained low.

[0055] Cyanobacteria cannot be consumed by shellfish, and the diatom content in the control group was too low. Therefore, the control group could not be used for the experiment of shellfish consuming diatoms.

[0056] S5: Construct shellfish farming ponds with dimensions of 4*3*0.5 meters (length*width*height). Add 55,000 shellfish per m³ to the ponds. 2 After the clams were added, the aquaculture wastewater containing diatoms, which had been treated in step S4, was added. It was determined that the diatom-rich aquaculture wastewater was utilized when it entered the clam and shellfish surface flow pool. The diatoms were completely utilized after the wastewater stayed in the shellfish aquaculture pool for 1 hour.

[0057] As can be seen from the above three embodiments, the content of elements such as nitrogen and phosphorus in aquaculture wastewater treated by the ecological purification method of aquaculture wastewater provided by the present invention is significantly reduced, and the treated aquaculture wastewater can be directly discharged.

[0058] Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some instances, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and employed by conventional methods. Unless otherwise stated, the use of commercially available reagents and instruments shall be performed according to the manufacturer's instructions and parameters.

[0059] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. A method for directional cultivation of diatoms using aquaculture effluent, characterized by, The method comprises the following steps: S1, precipitation: discharging the aquaculture tail water into a sedimentation tank to precipitate the silt and large particles; S2, sterilization and algae removal: irradiating the aquaculture tail water with ultraviolet rays of 254 nm to kill the bacteria and original algae in the aquaculture tail water; S3, nutrient structure adjustment: adjusting the salt content in the aquaculture tail water, wherein the parameters for adjusting the salt content in the aquaculture tail water include total salinity, silicate content, phosphate content and ammonium salt content, the total salinity is 20-30‰, the silicate content is 500-1000 μmol / L, the phosphate content is 0.6-0.9 mg / L, and the ammonium salt content is 4-6 mg / L; S4, algal species, bacteria inoculation and cultivation: diatoms and diatom symbiotic bacteria are inoculated into the aquaculture tail water, the diatom inoculation density is determined by the following parameters: the concentration of diatom chlorophyll in the aquaculture tail water is 300-500 μg / L, the diatom symbiotic bacteria are mixed bacteria of Marinobacter sp., Alteromonas macleodii 、 Muricauda sp, the planting density of the diatom symbiotic bacteria is 10 4 ~10 6 cell / mL, the illumination intensity is not less than 4000 lux, the illumination time is not less than 12 hours / day, and the cultivation is carried out for 3-7 days, wherein the diatom is Chaetoceros muelleri.

2. The method for directional culture of diatoms using aquaculture effluent according to claim 1, wherein, In the step S1, the precipitation time is greater than or equal to 24 hours.

3. The method for directional culture of diatoms using aquaculture effluent according to claim 1, wherein, Further comprising Step S5: constructing a shellfish aquaculture tank to mix culture of shellfish and the siliceous algae-containing aquaculture tail water treated in the step S4.

4. The method for directional culture of diatoms using aquaculture effluent according to claim 3, wherein, When the shellfish aquaculture tank is used for the mixed culture, the height of the shellfish aquaculture tank is not less than 20 cm.

5. The method for directional culture of diatoms using aquaculture effluent according to claim 4, wherein, The density of the shellfish in the culture tail water is 500,000-2,000,000 particles / m 2 .

6. The method for directional culture of diatoms using aquaculture effluent according to claim 5, wherein, The shellfish is selected from one or more of Sinonovacula constricta, Cyclotella meneghiniana, Cyclotella glomerata, Cyclotella atomus, Cyclotella kotschensis, Cyclotella comta, Cyclotella elliptica, Cyclotella meneghiniana, Cyclotella glomerata, Cyclotella atomus, Cyclotella kotschensis, Cyclotella comta, Cyclotella elliptica, Cyclotella meneghiniana, Cyclotella glomerata, Cyclotella atomus, Cyclotella kotschensis, Cyclotella comta, Cyclotella elliptica, Cyclotella meneghiniana, Cyclotella glomerata, Cyclotella atomus, Cyclotella kotschensis, Cyclotella comta, Cyclotella elliptica, Cyclotella meneghiniana, Cyclotella glomerata, Cyclotella atomus, Cyclotella kotschensis, Cyclotella comta, Cyclotella elliptica, Cyclotella meneghiniana, Cyclotella glomerata, Cyclotella atomus, Cyclotella kotschensis, Cyclotella comta, Cyclotella elliptica, Cyclotella meneghiniana, Cyclotella glomerata, Cyclotella atomus, Cyclotella kotschensis, Cyclotella comta, Cyclotella elliptica, Cyclotella meneghiniana, Cyclotella glomerata, Cyclotella atomus, Cyclotella kotschensis, Cyclotella comta, Cyclotella elliptica, Cyclotella meneghiniana, Cyclotella glomerata, Cyclotella atomus, Cyclotella kotschensis, Cyclotella comta, Cyclotella elliptica, Cyclotella meneghiniana, Cyclotella glomerata, Cyclotella atomus, Cyclotella kotschensis

Images