Kappaphycus polysaccharide as well as preparation method and application thereof in microalgae harvesting

Abstract

The invention discloses kappaphycus polysaccharide as well as a preparation method and application thereof in microalgae harvesting. Kappaphycus is used as a raw material, an extraction solution containing citric acid and calcium chloride is used for carrying out heating treatment on a frond body, and the Kappaphycus polysaccharide is obtained through ethanol flocculation and drying treatment. The invention provides an algae source flocculant without safety risk, which is prepared by using marine red algae-kappaphycus as a raw material, carrying out heating treatment on algae by using dilute citric acid and a low-concentration calcium chloride solution, carrying out ethanol flocculation and drying treatment to obtain kappaphycus polysaccharide powder, and dissolving kappaphycus polysaccharide by using 1% acetic acid to obtain the algae source flocculant without safety risk. And high-efficiency harvesting of different types of microalgae can be realized.

Description

Technical Field

[0001] This invention belongs to the field of microalgae, specifically relating to a Kappa algae polysaccharide, its preparation method, and its application in microalgae harvesting. Background Technology

[0002] Microalgae are a type of small, photosynthetic lower plant. They have significant development and utilization value in fields such as biopharmaceuticals, nutritional products, health products, bio-fertilizers, natural food processing, biological feed, wastewater treatment, and renewable energy production, and have attracted the attention of governments and scientists around the world.

[0003] Currently, only a limited number of microalgae species have been successfully cultivated on a large scale, including Spirulina, Dunaliella salina, Haematococcus pluvialis, Chlamydomonas reinhardtii, Micrococcus pluvialis, Chlorella vulgaris, Phaeodactylum tricornutum, and Phococcus pluvialis. Many microalgae with development value struggle to achieve industrialization, with harvesting technology being a key bottleneck. Harvesting microalgae using traditional methods accounts for approximately 35% of the cost of algae powder production. If algal cell density decreases, harvesting costs will increase further. Furthermore, the harvesting of many microalgae (such as microalgae) relies solely on energy-intensive and costly centrifugation processes. Therefore, developing an efficient and low-energy-consumption harvesting technology is urgently needed. Currently, the technologies used for large-scale microalgae harvesting mainly include: 1) Filtration method: This method requires simple equipment and can be achieved using sieves of specific specifications, resulting in low cost. However, this method is only suitable for harvesting filamentous algae, limiting its application. Some valuable spherical microalgae, such as *Microcystis aeruginosa* (rich in EPA) and *Dunaliella salina* (rich in β-carotene), cannot be harvested using this method at all; 2) Centrifugation method: This method is suitable for harvesting most algae. The required equipment is a centrifuge (such as a tubular centrifuge, a disc centrifuge, and a tripod centrifuge). It has been applied to the production of some economically valuable microalgae, such as *Chlorella vulgaris*. However, this method has disadvantages such as huge equipment investment, the need for dedicated personnel to maintain the equipment, and complex operating procedures; 3) Sedimentation method: This method is suitable for microalgae with larger cell volumes, such as the harvesting of red cells from *Haematococcus pluvialis*.

[0004] Flocculation harvesting technology has received significant attention in recent years, but it remains in the laboratory exploration stage and has yet to be commercialized. The principle of microalgae flocculation harvesting is to disrupt the stable suspension of algal cells in the culture medium. By reducing or neutralizing the surface charge of the algal cells, tiny algal cells aggregate to form larger flocs, which are then easily separated by gravity sedimentation or flotation. Most microalgae carry a negative surface charge and disperse uniformly under electrostatic repulsion. Flocculation is the process of overcoming this repulsive force. The main mechanisms include: 1) Charge neutralization: Adding positively charged flocculants (such as aluminum salts, iron salts, or cationic polymers) to the algal solution neutralizes the negative charge on the algal cell surface with their positively charged groups, reducing intercellular repulsion and causing aggregation through van der Waals forces; 2) Bridging: The active groups of long-chain polymeric flocculants (such as chitosan) can simultaneously adsorb multiple algal cells, forming "bridges" between cells and pulling them together to form flocs; 3) Netting and sweeping: Some flocculants (such as aluminum hydroxide precipitate) form huge net-like flocs during formation, which, during sedimentation, act like a filter, enveloping and sweeping away surrounding algal cells. Whether chemical, biological, or physical flocculation methods, the fundamental goal is to change the interfacial properties of algal cells, transforming "micron-sized cells" into "millimeter-sized flocs," thereby significantly improving subsequent separation efficiency.

[0005] In recent years, the core direction of microalgae flocculation harvesting technology has shifted from relying on traditional chemical flocculants to developing more efficient, environmentally friendly, and low-cost flocculation strategies. While traditional inorganic (such as aluminum and iron salts) and organic polymeric flocculants are effective, they suffer from problems such as metal ion residue pollution, large dosage requirements, and narrow applicability. Therefore, current research focuses on developing novel green flocculants, such as natural polymers like chitosan and modified starch products, as well as functional polymers with zwitterionic properties, which demonstrate advantages in reducing environmental impact and improving biosafety. Physical flocculation technology, especially electrocoagulation, achieves flocculation by generating metal hydroxides through an electric field, avoiding the direct addition of chemical reagents. Optimization of process parameters and innovation in electrode materials (such as using soluble anode combinations) have improved efficiency and reduced energy consumption; however, electrode passivation and energy consumption remain challenges for large-scale application. Bioflocculation utilizes microorganisms or their metabolites to induce microalgae aggregation. While aligning with sustainable development principles, its flocculation mechanism is complex, process controllability is poor, efficiency is unstable, and time-consuming. More importantly, research has abandoned reliance on single technologies and instead advocates for "combined processes" that couple multiple technologies. For example, preliminary concentration is achieved through flocculation (especially environmentally friendly biological or electroflocculation), followed by deep dehydration using energy-efficient centrifugation or flotation. This "two-step method" significantly reduces overall energy consumption and cost. Furthermore, obtaining superior algal strains with "self-flocculation" capabilities through algal selection, or inducing flocculation by regulating culture conditions (such as pH and nutrients), is considered a fundamental way to solve harvesting problems at their source.

[0006] Kappa algae is a large marine red alga and one of the world's most widely cultivated seaweeds. Its economic value mainly comes from carrageenan in its cell walls, which is widely used in the food, daily chemical, and pharmaceutical industries as a gelling agent, thickener, and stabilizer. Kappa algae polysaccharides are mostly sulfated galactans, with a basic backbone consisting of linear chains formed by alternating α-1,3 and β-1,4 glycosidic bonds of galactose or its derivatives. They exhibit good water solubility, can form colloidal solutions, and can form a three-dimensional network structure through molecular chain cross-linking. With slight modifications, they can become a natural and ideal microalgae flocculant. By bonding the anionic sulfate groups in the Kappa algae polysaccharide molecular chains with cations, a more stable network structure is formed at the molecular level. Simultaneously, the addition of excess cations imparts positive and negative charges to the polysaccharides. These cations bridge algal cells, causing them to precipitate and significantly improving flocculation and harvesting efficiency.

[0007] Among the currently published patents on "microalgae harvesting technology," those involving flocculation harvesting mainly include:

[0008] (1) A process for harvesting and reculturing microalgae using alkaline sedimentation (patent application number: 202510806811.9), which enables efficient microalgae cultivation and is suitable for autotrophic,

[0009] Heterotrophic and heterotrophic-autotrophic cultivation methods.

[0010] (2) A method for preparing cross-linked polyglutamic acid and its application in microalgae harvesting (patent application number: 202510658160.3). This patent uses polyglutamic acid fermentation broth that has been sterilized and salted out and reconstituted, or a solution prepared with polyglutamic acid powder as raw material. The pH is adjusted to a suitable range. Ethanol is added to the polyglutamic acid fermentation broth or the solution prepared with polyglutamic acid powder in a certain proportion. After stirring evenly, the paste precipitate is collected and weighed. The cross-linking agent is added to the paste precipitate in a suitable mass ratio with polyglutamic acid. After mixing evenly, it is spread evenly in a drying tray and placed in a vacuum drying equipment to dry to constant weight at a certain temperature. The product is crushed with a pulverizer and passed through a 40-mesh sieve to obtain the cross-linked polyglutamic acid product, which can be used for the flocculation harvesting of microalgae.

[0011] (3) A method for preparing and applying a chitosan-diatomaceous earth composite flocculant (patent application number: 202411893511.0). This invention discloses a method for preparing and applying a chitosan-diatomaceous earth composite flocculant. The method involves preparing a chitosan-diatomaceous earth flocculant using chitosan and diatomaceous earth as raw materials, and then adding γ-aminopropyltriethoxysilane (APTES) to prepare a composite flocculant (APTES-CTS / DTE). Compared with chitosan as a flocculant, the composite flocculant of this invention reduces the amount of chitosan used; compared with diatomaceous earth as a flocculant, its harvesting efficiency is significantly improved.

[0012] (4) A salt-tolerant modified cationic starch-based flocculant and its preparation method and its application in flocculating and harvesting microalgae (Patent Application No.: 202411840903.0). This invention discloses a salt-tolerant modified cationic starch-based flocculant and its preparation method and its application in flocculating and harvesting microalgae. The preparation method includes the following steps: 1) First, mix and stir an alkaline solution with starch, then add a modifier solution, dodecenyl succinic anhydride (DDSA), mix and react, and finally wash and dry to obtain modified starch; 2) First, mix and stir an alkaline solution with the modified starch obtained in step (1), then add glycidyltrimethylammonium chloride (GTA), mix and react, and finally wash and dry to obtain modified starch. This invention prepares a salt-tolerant modified cationic starch-based flocculant by cationizing and hydrophobically modifying starch with GTA and DDSA. This flocculant has good salt tolerance in microalgae flocculation and harvesting, and can still achieve a harvest rate of more than 80% under high salinity.

[0013] (5) Microalgae flocculant and method for harvesting microalgae (Patent Application No.: 202211233679.X), the present invention discloses a microalgae flocculant, including one or more small peptides. The invention also provides a method for harvesting microalgae, comprising: adding the microalgae flocculant to the algae solution to be harvested, and collecting the microalgae flocs after the microalgae have flocculated.

[0014] (6) A method for harvesting Chlorella using a flocculant (Patent Application No.: CN202311071670.8), this invention relates to the field of flocculation harvesting of Chlorella and other microalgae, specifically to a method for harvesting Chlorella using a flocculant, comprising the following steps: 1) Chlorella cultivation; 2) Ca-chitosan preparation; 3) Ca-chitosan grafting verification; 4) Ca-chitosan flocculation of Chlorella; by adjusting the pH of Chlorella using calcium hydroxide, under the synergistic effect of calcium ions and chitosan, it is possible to... While reducing the amount of chitosan used, the flocculation rate of Chlorella can be significantly improved. By modifying chitosan through chemical modification, Ca-chitosan is prepared as a flocculant, which greatly reduces the amount of Ca-chitosan used compared to using chitosan as a flocculant. By adjusting the pH of Chlorella from 9 to 8.5, the flocculation rate of Ca-chitosan is higher than that of chitosan under this pH condition, which can overcome the shortcomings of existing technologies that require large amounts of chitosan and have poor flocculation effect when harvesting Chlorella.

[0015] Analysis of the above-mentioned microalgae flocculation harvesting process revealed that it has drawbacks such as narrow application range, safety risks, immature technology, and inability to be used in large-scale production. In view of the above problems, this invention uses marine red algae - Kappa algae - as raw material and heats it with a dilute acid + low concentration calcium chloride solution to finally obtain a highly efficient algal flocculant. This flocculant has no safety risks, the preparation process is simple, and it can achieve low-cost and high-efficiency harvesting of microalgae.

[0016] Disadvantages of existing technology:

[0017] 1) Traditional microalgae harvesting processes typically utilize high-speed centrifugation. High-speed centrifuges are costly and energy-intensive, have low centrifugation efficiency, and require professional operation and maintenance. Furthermore, as the harvesting scale increases, the costs of centrifugation equipment and personnel will exceed the company's affordability.

[0018] 2) There are many types of microalgae in nature. Some small microalgae, such as "microalgae" and "microalgae", are difficult to harvest effectively. Low-cost filtration methods are only suitable for harvesting filamentous algae.

[0019] 3) Currently, there are many problems with microalgae flocculation harvesting technology. For example, many flocculants have serious safety issues (such as aluminum hydroxide), which limits the use of microalgae in food, feed, health products or pharmaceuticals. Different microalgae have different surface charges and extracellular polymer contents, which means that the same flocculant may be very effective for algae species A but completely ineffective for algae species B, lacking universality. Chemical flocculants have long reaction times and low flocculation efficiency, resulting in huge consumption of flocculants for large-scale harvesting. Summary of the Invention

[0020] To address the problems of "high harvesting cost and low harvesting efficiency of microalgae," this invention proposes a method using marine red algae, Kappa algae, as raw material. The algae are heated with a solution of dilute citric acid and low-concentration calcium chloride, followed by ethanol flocculation and drying to obtain Kappa algae polysaccharide powder. The Kappa algae polysaccharide is then dissolved in 1% acetic acid to obtain a safe algal flocculant that enables efficient harvesting of different types of microalgae.

[0021] The first object of this invention is to provide a Kappa algae polysaccharide, which is prepared by the following method:

[0022] Using Kappa algae as raw material, the algae were heated with an extraction solution containing citric acid and calcium chloride, and then subjected to ethanol flocculation and drying to obtain Kappa algae polysaccharide.

[0023] Preferably, the concentration of citric acid is 0.01 mol / L and the concentration of calcium chloride is 0.04 mol / L.

[0024] Preferably, the Kappa algae and the extract are mixed at a material-to-liquid ratio of 1:50 g / ml, and then heated at 80°C for 5 hours to obtain the Kappa algae polysaccharide extract.

[0025] Preferably, the ethanol flocculation involves adding Kappa algae polysaccharide to ethanol at a volume ratio of 1:4 to flocculate the Kappa algae polysaccharide, and then drying it using a freeze dryer to obtain Kappa algae polysaccharide.

[0026] The second objective of this invention is to provide a microalgae flocculant, which is obtained by dissolving the above-mentioned Kappa algae polysaccharide in acetic acid.

[0027] Preferably, it is dissolved in acetic acid with a mass fraction of 0.1-10%, and more preferably in acetic acid with a mass fraction of 0.1%.

[0028] A third objective of this invention is to provide the application of the aforementioned microalgae flocculant in flocculent microalgae.

[0029] Preferably, the microalgae flocculant is dissolved in acetic acid and then added to the microalgae solution to flocculate the microalgae.

[0030] Preferably, the acetic acid is acetic acid with a mass fraction of 0.1-10%.

[0031] Preferably, the microalgae flocculant is dissolved in acetic acid with a mass fraction of 0.1-10% and the material-to-liquid ratio is 1g:100ml. Then, the microalgae flocculant is added to the microalgae solution at a concentration of 10g / L to flocculate the microalgae.

[0032] Preferably, the microalgae solution has a concentration of 0.1-5 absorbance at OD750nm.

[0033] The microalgae solution can contain Chlorella, Spirulina, Porphyra yezoensis, Dunaliella salina, Haematococcus pluvialis, Phaeodactylum tricornutum, Isochrysis zhanjiangensis, Scenedesmus obliqueensis, Micrococcus pluvialis, and Euglena slenderis.

[0034] To address the shortcomings of existing technologies, this invention proposes a natural flocculant derived from *Kappa algae*, which enables low-cost and high-efficiency harvesting of microalgae. This technology has the following advantages:

[0035] 1) The technology provided by this invention can achieve low-cost and high-efficiency harvesting of microalgae without the need for high-cost and high-energy-consumption centrifugation equipment.

[0036] 2) The technology provided by this invention is applicable to the harvesting of different types of microalgae, and the harvesting efficiency can reach more than 95%.

[0037] 3) The technology provided by this invention does not pose any food safety or environmental safety risks. Attached Figure Description

[0038] Figure 1 The effect of different flocculant dosages on microalgae flocculation efficiency;

[0039] Figure 2 This study compares the flocculation effects of Kappa algae polysaccharide with those of commercially available λ-type carrageenan and alginate.

[0040] Figure 3 The difference between Kappa algae polysaccharide flocculant and the flocculant of different types of microalgae;

[0041] Figure 4 The effect of different flocculant preparation methods on microalgae flocculation;

[0042] Figure 5 A comparison of the flocculation effects of different types of algal polysaccharides Detailed Implementation

[0043] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to specific embodiments.

[0044] Example 1: Preparation and flocculation process of Kappa algae polysaccharide under optimal conditions

[0045] 1) Weigh 1 kg of Kappa algae with a water content of about 60% as raw material to extract Kappa algae polysaccharides. Prepare an extraction solution with a citric acid concentration of 0.01 mol / L and a calcium chloride concentration of 0.04 mol / L. Mix the Kappa algae and the extraction solution at a ratio of 1:50 g / mL, heat at 80℃ for 5 hours, filter through a 200-mesh silk sieve to remove algal residue, and obtain Kappa algae polysaccharide extract. The absorbance of the polysaccharide extract at a wavelength of 750 nm is 0.02, indicating high clarity.

[0046] 2) Ethanol was added to the extract of Kappa algae polysaccharide at a volume ratio of 1:4 to flocculate the Kappa algae polysaccharide. The polysaccharide was then dried using a freeze dryer to obtain Kappa algae polysaccharide powder. A total of about 100 grams of powder was obtained, and the polysaccharide yield was calculated to be about 10%.

[0047] 3) Weigh 1.0 g of Kappa algae polysaccharide powder, add 100 mL of 1% acetic acid, and dissolve it completely to obtain a colorless, viscous, and transparent microalgae flocculant with a concentration of 10 g / L.

[0048] 4) Take 1L of Chlorella algal solution with an absorbance of 2.0 at 750 nm wavelength, add 10 mL of flocculant, stir thoroughly, and let stand for 10 minutes until the algal cells form flocs.

[0049] 5) Filter the algae solution through a 400-mesh silk sieve to obtain wet algae mud.

[0050] Example 2: Differences in the microalgal flocculation of Kappa polysaccharides prepared by different methods

[0051] To verify the flocculation effect of Kappa algae polysaccharide prepared under different citric acid and calcium chloride concentrations on microalgae, this experiment set up different combinations of citric acid and calcium chloride concentrations: citric acid concentrations of 0, 0.001, 0.01, 0.05, 0.1, and 0.5 mol / L, and calcium chloride concentrations of 0, 0.02, 0.04, 0.1, 0.5, and 1.0 mol / L, and conducted an orthogonal experiment (Table 1). The obtained extract was used to prepare flocculants according to steps 2) and 3) of Example 1. Chlorella was used as the experimental material. The absorbance of Chlorella at 750 nm was 1.0. The algal solution in each experimental group was 100 mL, and 1 mL of flocculant was added to each experimental group. After standing for 10 minutes, the supernatant was taken and the absorbance at 750 nm was measured. The flocculation efficiency of the microalgae was calculated according to the following formula:

[0052] Flocculation efficiency (%) = (Absorbance of supernatant at 750 nm / Absorbance of original algal solution at 750 nm) × 100%

[0053] Table 1

[0054] As shown in Table 1, when the concentration of citric acid is 0.01 mol / L and the concentration of calcium chloride is 0.04 mol / L, the obtained Kappa algae polysaccharide flocculant has the highest flocculation efficiency of 98.5%. The other groups can also achieve flocculation, but the effect is poor and they are not suitable for use.

[0055] Example 3: Effect of different flocculant dosages on microalgae flocculation

[0056] Following steps 1), 2), and 3) of Example 1, a microalgae flocculant with a concentration of 10 g / L was obtained. Chlorella was used as the experimental material. The absorbance of Chlorella at 750 nm was 1.0. Each experimental group contained 100 mL of algal solution. 0.1, 0.2, 0.6, 0.8, 1.0, 1.5, 3.0, 6.0, 8.0, and 10 mL of flocculant were added to each group (corresponding to actual flocculant addition amounts of 1, 2, 6, 8, 10, 15, 30, 60, 80, and 100 mg). After standing for 10 minutes, the supernatant was collected and its absorbance at 750 nm was measured. The flocculation efficiency of the microalgae was calculated. Figure 1 As shown, the optimal flocculation effect of 98.5% was obtained when the addition amount was 1.0 mL.

[0057] Example 4: Comparison of the flocculation effects of Kappa polysaccharide with commercially available λ-carrageenan and alginate.

[0058] To compare the flocculation effects of commercially available λ-carrageenan and alginate with the flocculant of this invention, a microalgae flocculant with a concentration of 10 g / L was obtained following steps 1), 2), and 3) of Example 1. λ-carrageenan and alginate were purchased and prepared into solutions with concentrations of 1, 5, and 10 g / L, respectively. Chlorella vulgaris was used as the experimental material, with an absorbance of 1.0 at 750 nm. Each experimental group contained 100 mL of algal solution, and 1 mL of flocculant was added to each group. After standing for 10 minutes, the supernatant was collected and its absorbance at 750 nm was measured. The flocculation efficiency of the microalgae was calculated. Figure 2 As shown, commercially available λ-type carrageenan and alginate have almost no flocculation effect, which is likely related to their preparation process.

[0059] Example 5: Differences in the flocculation of different types of microalgae by Kappa algae polysaccharide flocculant

[0060] To verify the universality of the Kappa algae polysaccharide flocculant in this invention for different microalgae, we selected 10 microalgae of different sizes, growth environments (seawater and freshwater), and morphologies (spherical, filamentous, and spindle-shaped) for verification. The 10 microalgae are described below: 1) Chlorella vulgaris, freshwater, spherical, 3-5 micrometers; 2) Spirulina, freshwater, spiral-shaped, 100-200 micrometers; 3) Porphyromonas purpureus, seawater, spherical, 3-5 micrometers; 4) Dunaliella salina, seawater, spherical, 10... -15 micrometers; 5) Haematococcus pluvialis, freshwater, spherical, 30-50 micrometers; 6) Brown finger algae, seawater, irregular shape, 10 micrometers; 7) Isochrysis zhanjiangensis, seawater, spherical, 4-6 micrometers; 8) Scenedesmus oblique, freshwater, fusiform, cell length 10-21 micrometers, width 3-9 micrometers; 9) Micrococcus pluvialis, seawater, spherical, 3-5 micrometers; 10) Euglena slenderis, freshwater, cylindrical or fusiform, length 36-39 micrometers, width 11-13 micrometers.

[0061] Following steps 1), 2), and 3) of Example 1, a microalgae flocculant was obtained at a concentration of 10 g / L. Ten microalgae species were used as experimental materials, with an absorbance of 1.0 at 750 nm. Each experimental group contained 100 mL of algal solution, and 1 mL of flocculant was added to each group. After standing for 10 minutes, the supernatant was collected, and the absorbance at 750 nm was measured. The flocculation efficiency of the microalgae was calculated. Figure 3 As shown, the flocculation efficiency of all 10 microalgae can reach over 95%, indicating that the flocculant developed in this invention has universal applicability.

[0062] Example 6: Effects of different flocculant preparation methods on microalgae flocculation

[0063] This invention uses 1% acetic acid to prepare a microalgae flocculant, achieving the best microalgae flocculation effect. Specific data supporting this superior method are as follows: 1 gram of Kappa algae polysaccharide powder (prepared according to Example 1, steps 1 and 2) was weighed and added to 100 mL of acetic acid solutions with mass fractions of 0.1%, 0.5%, 1%, 2%, 5%, and 10%, respectively. Microalgae flocculants prepared with 100 mL of deionized water, 0.1% hydrochloric acid, 1% hydrochloric acid, 0.1% sulfuric acid, and 1% sulfuric acid were used as controls. The flocculant concentration in all treatment groups was 10 g / L. Chlorella was used as the experimental material, with an absorbance of 1.0 at 750 nm. Each experimental group contained 100 mL of algal solution, and 1 mL of flocculant was added to each group. After standing for 10 minutes, the supernatant was collected, and the absorbance at 750 nm was measured. The flocculation efficiency of the microalgae was calculated. Figure 4 As shown, flocculants prepared with 1% acetic acid have the best effect, while concentrations exceeding 1% have virtually no significant impact. Flocculants prepared with water, hydrochloric acid, and sulfuric acid as solvents have absolutely no flocculation effect on Chlorella.

[0064] Example 7: Effect of different algal cell densities on flocculation harvesting

[0065] The microalgal flocculant was obtained according to steps 1), 2), and 3) of Example 1, with a concentration of 10 g / L. Chlorella was used as the experimental material. The absorbance values ​​of Chlorella at 750 nm were 0.1, 0.5, 1.0, 2.0, 3.0, and 5.0. In large-scale cultivation, the maximum absorbance value of Chlorella at 750 nm was usually lower than 5.0. The algal solution in each experimental group was 100 mL. 1 mL of microalgal flocculant was added to each experimental group and allowed to stand for 10 minutes. The absorbance value of the supernatant at 750 nm was measured, and the flocculation efficiency of the microalgae was calculated. As shown in Table 2, the flocculation efficiency decreased slightly with the increase of algal cell density, but it could still reach more than 95%.

[0066] Table 2

[0067] Example 8 Comparison of flocculation effects of different types of algal polysaccharides

[0068] Kappa algae, Chlorella, Spirulina, Euglena, Haematococcus pluvialis, Ulva, kelp, Sargassum, and Porphyra were selected as experimental materials. Among them, Chlorella, Spirulina, Euglena, and Haematococcus pluvialis are microalgae, while Kappa algae, Ulva, kelp, Sargassum, and Porphyra are macroalgae. Flocculants from different sources were obtained according to steps 1), 2), and 3) of Example 1, namely flocculant 0 (Kappa algae polysaccharide), flocculant 1 (Chlorella polysaccharide), flocculant 2 (Spirulina polysaccharide), flocculant 3 (Euglena polysaccharide), flocculant 4 (Haematococcus pluvialis polysaccharide), flocculant 5 (Ulva polysaccharide), flocculant 6 (kelp polysaccharide), flocculant 7 (Sargassum polysaccharide), and flocculant 8 (Porphyra polysaccharide), with a concentration of 10 g / L. Chlorella was used as the experimental material, with an absorbance of 1.0 at 750 nm. The algal solution in each experimental group was 100 g / L. 1 mL of flocculant was added to each experimental group, and the mixture was allowed to stand for 10 minutes. The supernatant was then measured at 750 nm to calculate the microalgae flocculation efficiency. Figure 5 As shown, apart from flocculants 7 and 8 having some flocculation effect, the other algal polysaccharide treatment groups had no flocculation effect.

Claims

1. A method for preparing kappa-carrageenan, characterized in that, It comprises the following steps: The kappa algae is used as raw material, and the algae body is heated and treated by using an extraction solution containing citric acid and calcium chloride, and then ethanol flocculation and drying treatment are performed to obtain the kappa algae polysaccharide.

2. The production method according to claim 1, characterized by, The concentration of the citric acid is 0.01 mol / L, and the concentration of the calcium chloride is 0.04 mol / L.

3. The production method according to claim 1, characterized by, The kappa algae and the extraction solution are mixed according to a solid-liquid ratio of 1:50 g / ml, heated extraction is performed at 80 DEG C for 5 hours to obtain the kappa algae polysaccharide extraction solution.

4. The production method according to claim 1 or 3, characterized by, The ethanol flocculation is performed by adding ethanol to the kappa algae polysaccharide extraction solution according to a volume ratio of 1:4, flocculating the kappa algae polysaccharide, and drying by using a freeze dryer to obtain the kappa algae polysaccharide.

5. A kappa algae polysaccharide prepared by the preparation method according to claim 1, 2, 3 or 4.

6. A microalgal flocculant, characterized by, The kappa algae polysaccharide according to claim 5 is dissolved by using acetic acid to obtain a microalgae flocculant.

7. The microalgal flocculant according to claim 6, characterized in that, The acetic acid has a mass fraction of 0.1-10%, preferably a mass fraction of 0.1%.

8. The microalgae flocculant according to claim 5 is used for flocculating microalgae.

9. Use according to claim 8, characterized in that, The microalgae flocculant is dissolved by using acetic acid and then added to a microalgae liquid to flocculate the microalgae, preferably, the acetic acid has a mass fraction of 0.1-10%, further preferably, the microalgae flocculant is dissolved by using acetic acid with a mass fraction of 0.1-10%, a solid-liquid ratio of 1 g:100 ml, and then the microalgae flocculant is added to the microalgae liquid to flocculate the microalgae according to a concentration of 10 g / L.

10. Use according to claim 9, characterized in that, The microalgae liquid has an absorbance of 0.1-5 at OD750 nm, preferably, the microalgae liquid is a liquid of Chlorella vulgaris, Spirulina platensis, Porphyridium purpureum, Dunaliella salina, Haematococcus pluvialis, Phaeodactylum tricornutum, Isochrysis zhanjiangensis, Scenedesmus obliquus, Nannochloropsis, and Euglena gracilis.

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