Application of a cationic polymer compound bentonite flocculation to collect wide salinity microalgae and a collection method

Abstract

This invention discloses an application and harvesting method for wide-salinity microalgae harvesting using a cationic polymer-compounded bentonite flocculation technique, belonging to the field of environmental protection technology. The method includes the following steps: adding polydimethyldiallyl ammonium chloride solution and sodium bentonite suspension to the algal solution according to the cell biomass of the microalgae to be harvested, stirring, and collecting by sedimentation to complete the harvest. This invention achieves efficient flocculation harvesting of microalgae in wide-salinity environments by using a combination of PDDAC and BE, achieving a harvest rate of over 90% within a salinity range of 0‰ to 40‰. It features high flocculation efficiency, low flocculant dosage, large and compact floc size, and significant salt resistance. It is suitable for efficient harvesting of microalgae from artificially cultivated or natural water bodies under wide salinity conditions, providing a key technology for the field of microalgae harvesting and possessing broad application prospects. It solves the problems of poor salinity tolerance of flocculants, high flocculant dosage, and poor harvesting effect in current microalgae flocculation harvesting methods.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, specifically to the application and harvesting method of a cationic polymer compounded with bentonite for flocculation harvesting of microalgae with wide salinity. Background Technology

[0002] Microalgae are considered primary producers in water bodies, exhibiting high photosynthetic efficiency, rapid growth rates, and strong environmental adaptability. They are widely distributed in freshwater, brackish water, and marine water bodies, such as rivers, lakes and ponds (salinity less than 0.5‰), saline-alkali water bodies (salinity 1‰-10‰), estuaries (salinity 0.5‰-30‰), inland salt lakes (salinity 3‰-30‰), salt marshes (salinity 10‰-35‰), and oceans (salinity 10‰-40‰). They possess both resource and pollution potential. Microalgae, with their low concentration (less than 1.0 g / L), small size (3-30 µm), density close to water (1.07-1.14 g / m³), and negatively charged cell surfaces (-10 to 35 mV), can stably disperse in algal solutions. Therefore, efficient separation of microalgae from water is essential for both environmental remediation and resource utilization. Compared to methods such as natural sedimentation, mechanical retrieval, membrane separation, and centrifugation, flocculation has attracted much attention due to its advantages of simple operation, low cost, rapid and efficient operation, and ease of combination with other methods. Flocculation achieves algal cell aggregation and enlargement through charge neutralization, adsorption bridging, and netting / sweeping between flocculants and algal cells, forming flocs that then settle and achieve algal-water separation. Traditional flocculants are mainly divided into inorganic flocculants (such as iron salts and aluminum salts) and organic polymeric flocculants (such as polyacrylamide CPAM), but they are generally unsuitable for flocculating microalgae in medium- and high-salinity waters. This is mainly because: firstly, the high ionic strength in saline environments can shield the charged points of both the flocculant and the microalgae, inhibiting charge neutralization; secondly, the high ionic strength can reduce the repulsive forces within the polymer, causing the polymeric flocculant molecules to curl, thus weakening the adsorption bridging effect. Therefore, there is an urgent need to develop a highly efficient microalgae flocculation reagent and method that is tolerant to a wide range of salinity.

[0003] Compound flocculation can integrate the performance of multiple single flocculants, effectively compensate for the shortcomings of single flocculants, and achieve synergistic effects. It is a promising and effective method for obtaining microalgae flocculants with wide salinity tolerance. Examples include: organic-inorganic flocculant combination: Pan Gang et al. proposed using amphoteric starch and polyaluminum chloride in combination to achieve efficient flocculation and harvesting of microalgae over a wide salinity range; loaded flocculation: flocculants and loaders are used in combination (insoluble solid particles as loaders), utilizing the gravity settling or magnetic and adsorption effects of the loader to accelerate floc formation and sedimentation, including microsand and magnetic loaded flocculation; microparticle flocculation: microparticle retention systems in the wet end of papermaking can also be considered a special type of flocculation system. Unlike loaded flocculation, this system exerts a gravitational effect on the microparticle components. The settling performance requirement is not high, and it often depends on the interaction between the flocculant and the pre-flocculated particles formed by the pulp. The synergistic effect of different flocculants, particles and flocculated objects varies greatly. For example, in the wet end of papermaking, CPAM is usually used in combination with bentonite (BE), and cationic starch is used in combination with nano-silica sol. Moreover, there are high requirements for the structural properties of flocculants and particles. At present, there are also studies on the combination of chitosan and BE to adsorb heavy metals, remove glyphosate (a common herbicide) from aqueous solutions and remove natural dyes.

[0004] However, the flocculation efficiency of cationic polymers such as CPAM used in compound flocculants relies on the bridging effect of their ultra-high molecular weight (approximately 8-15 million). In high-salinity environments, due to the high ionic strength, the excessive coiling of CPAM molecular chains significantly weakens the bridging effect. Furthermore, the small number of cationic groups lose their charge due to charge shielding, making it difficult to meet the harvesting requirements in even higher salinity environments. Therefore, a method capable of meeting the flocculation and harvesting needs of microalgae under varying salinity conditions, including high-salinity environments, urgently needs to be developed. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide an application and harvesting method for wide-salinity microalgae harvesting using cationic polymer compound bentonite flocculation, thereby solving the problem that existing compound flocculants used for microalgae harvesting have poor harvesting effects in high-salinity environments and cannot achieve efficient flocculation harvesting under wide-salinity conditions.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] In a first aspect, the present invention provides an application of a cationic polymer compounded with bentonite for flocculation and harvesting of microalgae with broad salinity, wherein the cationic polymer is polydimethyldiallylammonium chloride and the bentonite is sodium bentonite.

[0008] Furthermore, when harvesting microalgae through flocculation, the dosage of polydimethyldiallyl ammonium chloride is 0.2 wt%-1.0 wt% of the biomass of the algal cells to be harvested, and the dosage of bentonite is 0.6 wt%-10 wt% of the biomass of the algal cells to be harvested.

[0009] A second aspect of the present invention provides a method for harvesting microalgae with a wide salinity range by flocculation of cationic polymers and bentonite, comprising the following steps:

[0010] Add polydiallyl ammonium chloride solution and sodium bentonite suspension according to the biomass of microalgae cells to be harvested, stir, collect by sedimentation, and complete the harvest.

[0011] Furthermore, the microalgal cell biomass was determined using the following methods:

[0012] A certain volume of microalgae sample was filtered using a 0.45 μm microporous membrane. The membrane was dried to constant weight and weighed before and after filtration. After filtration, the membrane was dried in an oven to constant weight and weighed again. The difference between the two weight measurements was divided by the filtration volume to obtain the microalgae cell biomass concentration (g / L). The measurement was repeated three times, and the average value was taken. Then, the microalgae cell biomass was calculated based on the volume of algae to be harvested.

[0013] Furthermore, the concentration of the polydimethyldiallylammonium chloride solution is 1-2 g / L, and the concentration of the sodium bentonite suspension is 5-15 g / L.

[0014] Furthermore, the amount of polydimethyldiallylammonium chloride added is 0.2 wt%-1.0 wt% of the biomass of the algal cells to be harvested, and the amount of bentonite added is 0.6 wt%-10 wt% of the biomass of the algal cells to be harvested.

[0015] Further, first add a polydimethyldiallylammonium chloride solution, then add a sodium bentonite suspension.

[0016] Further, after adding the polydiallylammonium chloride solution and stirring for 1-5 minutes, sodium bentonite suspension is added.

[0017] Furthermore, before adding the polydiallyl ammonium chloride solution, the algal solution is first stirred at 150-250 rpm for 1-3 minutes, then stirred at 40-60 rpm. After adding the polydiallyl ammonium chloride solution within 30-90 seconds, the algal solution is stirred at 150-250 rpm for 1-3 minutes to ensure uniform dispersion of the agent, then stirred at 40-60 rpm. Sodium bentonite suspension is added within 30-90 seconds, and the algal solution is first stirred at 150-250 rpm for 1-3 minutes to ensure uniform dispersion of the agent, then stirred at 40-60 rpm for 1-10 minutes, after which stirring is stopped to allow sedimentation.

[0018] Furthermore, the settling time is 5-15 minutes.

[0019] The present invention has the following beneficial effects:

[0020] This invention provides a method for harvesting microalgae under wide salinity conditions by combining polydiallyldiammonium chloride (PDDAC) with sodium bentonite (BE) through flocculation. This method achieves efficient flocculation and harvesting of microalgae within a salinity range of 0‰ to 40‰, with a harvest rate exceeding 90%. The method exhibits high flocculation efficiency, low flocculant dosage, and large, compact flocs with significant salt resistance. It is suitable for the efficient harvesting of microalgae from artificially cultivated or natural water bodies under relatively wide salinity conditions, providing a key technology for the field of microalgae harvesting and possessing broad application prospects. Attached Figure Description

[0021] Figure 1 The graph shows the changes in the harvest rate of flocculated microalgae with dosage under a salinity of 5‰ for PDDAC alone, BE alone, and PDDAC combined with BE. In the graph, (A) is PDDAC alone, (B) is BE alone, and (C) is PDDAC combined with BE.

[0022] Figure 2 The images show the sedimentation effect and microscopic morphology of the flocs formed after flocculation of microalgae under a salinity of 5‰. (A) is the sedimentation effect image, and (B) is the microscopic morphology image.

[0023] Figure 3 The graph shows the changes in the harvest rate of flocculated microalgae with dosage under a salinity of 10‰ for PDDAC alone, BE alone, and PDDAC combined with BE. In the graph, (A) is PDDAC alone, (B) is BE alone, and (C) is PDDAC combined with BE.

[0024] Figure 4 The images show the sedimentation effect and microscopic morphology of the flocs formed after flocculation of microalgae under a salinity of 10‰. (A) is the sedimentation effect image, and (B) is the microscopic morphology image.

[0025] Figure 5 The graph shows the changes in the harvest rate of flocculated microalgae with dosage under a salinity of 20‰ for PDDAC alone, BE alone, and PDDAC combined with BE. In the graph, (A) is PDDAC alone, (B) is BE alone, and (C) is PDDAC combined with BE.

[0026] Figure 6 The images show the sedimentation effect and microscopic morphology of the flocs formed after flocculating microalgae under a salinity of 20‰. (A) is the sedimentation effect image, and (B) is the microscopic morphology image.

[0027] Figure 7The graph shows the changes in the harvest rate of flocculated microalgae with dosage under a salinity of 30‰ for PDDAC alone, BE alone, and PDDAC combined with BE. In the graph, (A) is PDDAC alone, (B) is BE alone, and (C) is PDDAC combined with BE.

[0028] Figure 8 The images show the sedimentation effect and microscopic morphology of the flocs formed after flocculation of microalgae under a salinity of 30‰. (A) is the sedimentation effect image, and (B) is the microscopic morphology image.

[0029] Figure 9 The graph shows the changes in the harvest rate of flocculated microalgae with dosage under a salinity of 40‰ for PDDAC alone, BE alone, and PDDAC combined with BE. In the graph, (A) is PDDAC alone, (B) is BE alone, and (C) is PDDAC combined with BE.

[0030] Figure 10 The images show the sedimentation effect and microscopic morphology of the flocs formed after flocculating microalgae under a salinity of 40‰. (A) is the sedimentation effect image, and (B) is the microscopic morphology image.

[0031] Figure 11 A comparison chart of the harvest rates of the harvesting methods in Example 1 (PDDAC+BE) and Comparative Example 3 (BE+PDDAC) under different salinity conditions;

[0032] Figure 12 The diagram shows the harvest rate of microalgae harvested from CPAM and BE, where (A) represents a salinity of 30‰ and (B) represents a salinity of 40‰.

[0033] Figure 13 The floc size, strength factor, and recovery factor of PDDAC alone and PDDAC combined with BE to form flocs of microalgae are given, where (A) is PDDAC alone and (B) is PDDAC+BE.

[0034] Figure 14 A schematic diagram showing the optimal dosage and sedimentation effect of PDDAC combined with BE for harvesting microalgae under salinity of 5‰-40‰. Detailed Implementation

[0035] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0036] The main drugs used in the examples are as follows:

[0037] Cationic polyacrylamide, molecular weight 8-10 million, ionicity 30-35% (Shanghai Maclean Biochemical Technology Co., Ltd.); polydimethyldiallyl ammonium chloride, molecular weight 200,000, concentration 20% (Shanghai Aladdin Biochemical Technology Co., Ltd.); sodium bentonite (analytical grade, Tianjin Huasheng Chemical Reagent Co., Ltd.); experimental microalgae: common Chlorella vulgaris (…). Chlorella vulgaris Purchased from Yangzhou Shanze Biotechnology Co., Ltd., the basic properties of the microalgae are as follows: OD 685 The absorbance at 685 nm was 1.500±0.003, the pH was 7.0±0.3, the salinity was 5.0±0.1‰, and the algal cell biomass was 0.975±0.058 g / L. The salinity of the algal solution was adjusted by adding sodium chloride to obtain microalgae samples with different salinities, while ensuring that other basic properties of the microalgae samples remained unchanged.

[0038] Example 1:

[0039] A method for harvesting microalgae from cationic polymer-blended bentonite under 5‰ algal solution salinity conditions includes the following steps:

[0040] (1) The salinity of the algal solution to be harvested was adjusted to 5‰ by adding sodium chloride as the sample of algal solution to be harvested in this embodiment;

[0041] (2) Prepare a 1.5 g / L polydiallyl ammonium chloride (PPDAC) solution and a 10 g / L sodium bentonite (BE) suspension;

[0042] (3) Stir the algal solution sample obtained in step (1) at 200 rpm for 2 min, then at 50 rpm, add PPDAC solution within 1 min to make the concentration of PPDAC in the algal solution 0.4 mg / L, then stir again at 200 rpm for 2 min to make the agent evenly dispersed, then stir at 50 rpm, add BE suspension within 1 min to make the concentration of BE in the algal solution 6 mg / L, continue to stir at 200 rpm for 2 min to make the agent evenly dispersed, stir at 50 rpm for 5 min, let it settle for 10 min, pour off the supernatant, collect the settled microalgal flocs, dry and dehydrate to obtain microalgal powder.

[0043] Example 2:

[0044] A method for harvesting microalgae from cationic polymer-blended bentonite under 10‰ algal solution salinity conditions includes the following steps:

[0045] (1) The salinity of the algal solution to be harvested was adjusted to 10‰ by adding sodium chloride as the sample of algal solution to be harvested in this embodiment;

[0046] (2) Prepare a 1.5 g / L polydiallyl ammonium chloride (PPDAC) solution and a 10 g / L sodium bentonite (BE) suspension;

[0047] (3) Stir the algal solution sample obtained in step (1) at 200 rpm for 2 min, then at 50 rpm, add PPDAC solution within 1 min to make the concentration of PPDAC in the algal solution 0.4 mg / L, then stir again at 200 rpm for 2 min to make the agent evenly dispersed, then stir at 50 rpm, add BE suspension within 1 min to make the concentration of BE in the algal solution 10 mg / L, continue to stir at 200 rpm for 2 min to make the agent evenly dispersed, stir at 50 rpm for 5 min, let it settle for 10 min, pour off the supernatant, collect the settled microalgal flocs, dry and dehydrate to obtain microalgal powder.

[0048] Example 3:

[0049] A method for harvesting microalgae from cationic polymer-blended bentonite under algal solution salinity conditions of 20‰ includes the following steps:

[0050] (1) The salinity of the algal solution to be harvested was adjusted to 20‰ by adding sodium chloride as the sample of algal solution to be harvested in this embodiment;

[0051] (2) Prepare a 1.5 g / L polydiallyl ammonium chloride (PPDAC) solution and a 10 g / L sodium bentonite (BE) suspension;

[0052] (3) Stir the algal solution sample obtained in step (1) at 200 rpm for 2 min, then at 50 rpm, add PPDAC solution within 1 min to make the concentration of PPDAC in the algal solution 0.5 mg / L, then stir again at 200 rpm for 2 min to make the agent evenly dispersed, then stir at 50 rpm, add BE suspension within 1 min to make the concentration of BE in the algal solution 10 mg / L, continue to stir at 200 rpm for 2 min to make the agent evenly dispersed, stir at 50 rpm for 5 min, let it settle for 10 min, pour off the supernatant, collect the settled microalgal flocs, dry and dehydrate to obtain microalgal powder.

[0053] Example 4:

[0054] A method for harvesting microalgae from cationic polymer-blended bentonite under algal solution salinity conditions of 30‰ includes the following steps:

[0055] (1) The salinity of the algal solution to be harvested was adjusted to 30‰ by adding sodium chloride as the sample of algal solution to be harvested in this embodiment;

[0056] (2) Prepare a 1.5 g / L polydiallyl ammonium chloride (PPDAC) solution and a 10 g / L sodium bentonite (BE) suspension;

[0057] (3) Stir the algal solution sample obtained in step (1) at 200 rpm for 2 min, then at 50 rpm, add PPDAC solution within 1 min to make the concentration of PPDAC in the algal solution 0.5 mg / L, then stir again at 200 rpm for 2 min to make the agent evenly dispersed, then stir at 50 rpm, add BE suspension within 1 min to make the concentration of BE in the algal solution 30 mg / L, continue to stir at 200 rpm for 2 min to make the agent evenly dispersed, stir at 50 rpm for 5 min, let it settle for 10 min, pour off the supernatant, collect the settled microalgal flocs, dry and dehydrate to obtain microalgal powder.

[0058] Example 5:

[0059] A method for harvesting microalgae from cationic polymer-blended bentonite under 40‰ algal solution salinity conditions includes the following steps:

[0060] (1) The salinity of the algal solution to be harvested was adjusted to 40‰ by adding sodium chloride as the sample of algal solution to be harvested in this embodiment;

[0061] (2) Prepare a 1.5 g / L polydiallyl ammonium chloride (PPDAC) solution and a 10 g / L sodium bentonite (BE) suspension;

[0062] (3) Stir the algal solution sample obtained in step (1) at 200 rpm for 2 min, then at 50 rpm, add PPDAC solution within 1 min to make the concentration of PPDAC in the algal solution 0.5 mg / L, then stir again at 200 rpm for 2 min to make the agent evenly dispersed; then stir at 50 rpm, add BE suspension within 1 min to make the concentration of BE in the algal solution 60 mg / L, then stir at 200 rpm for 2 min to make the agent evenly dispersed, finally stir at 50 rpm for 5 min, let it settle for 10 min, pour off the supernatant, collect the settled microalgal flocs, dry and dehydrate to obtain microalgal powder.

[0063] Comparative Example 1:

[0064] A method for harvesting microalgae using PDDAC alone under 5‰ algal solution salinity conditions includes the following steps:

[0065] (1) The salinity of the algal solution to be harvested was adjusted to 5‰ by adding sodium chloride as the sample of algal solution to be harvested in this embodiment;

[0066] (2) Prepare a 1.5 g / L polydiallyl ammonium chloride (PPDAC) solution;

[0067] (3) Stir the algal solution sample obtained in step (1) at 200 rpm for 2 min, then at 50 rpm. Add PPDAC solution within 1 min to make the concentration of PPDAC in the algal solution 0.2 mg / L. Continue stirring at 200 rpm for 2 min to make the agent evenly dispersed. After stirring at 50 rpm for 5 min, let it settle for 10 min, pour off the supernatant, collect the settled microalgal flocs, dry and dehydrate to obtain microalgal powder.

[0068] Comparative Example 2:

[0069] A method for harvesting microalgae using BE alone under 5‰ algal solution salinity conditions includes the following steps:

[0070] (1) The salinity of the algal solution to be harvested was adjusted to 5‰ by adding sodium chloride as the sample of algal solution to be harvested in this embodiment;

[0071] (2) Prepare a 1.5 g / L polydiallyl ammonium chloride (PPDAC) solution and a 10 g / L sodium bentonite (BE) suspension;

[0072] (3) Stir the algal solution sample obtained in step (1) at 200 rpm for 2 min, then at 50 rpm, add BE suspension within 1 min to make the concentration of BE in the algal solution 2 mg / L, continue stirring at 200 rpm for 2 min to make the agent evenly dispersed, stir at 50 rpm for 5 min, let it settle for 10 min, pour off the supernatant, collect the settled microalgal flocs, dry and dehydrate to obtain microalgal powder.

[0073] Comparative Example 3:

[0074] A method for harvesting microalgae from cationic polymer-blended bentonite under 5‰ algal solution salinity conditions includes the following steps:

[0075] (1) The salinity of the algal solution to be harvested was adjusted to 5‰ by adding sodium chloride as the sample of algal solution to be harvested in this embodiment;

[0076] (2) Prepare a 1.5 g / L polydiallyl ammonium chloride (PPDAC) solution and a 10 g / L sodium bentonite (BE) suspension;

[0077] (3) Stir the algal solution sample obtained in step (1) at 200 rpm for 2 min, then at 50 rpm, add BE suspension within 1 min to make the concentration of BE in the algal solution 6 mg / L, then stir again at 200 rpm for 2 min to make the agent evenly dispersed, then stir at 50 rpm, add PPDAC solution within 1 min to make the concentration of PPDAC in the algal solution 0.4 mg / L, continue to stir at 200 rpm for 2 min to make the agent evenly dispersed, stir at 50 rpm for 5 min, let it settle for 10 min, pour off the supernatant, collect the settled microalgal flocs, dry and dehydrate to obtain microalgal powder.

[0078] Comparative Example 4:

[0079] A method for harvesting microalgae from cationic polymer-blended bentonite under algal solution salinity conditions of 30‰ includes the following steps:

[0080] (1) The salinity of the algal solution to be harvested was adjusted to 30‰ by adding sodium chloride as the sample of algal solution to be harvested in this embodiment;

[0081] (2) Prepare a 1.5 g / L polyacrylamide (CPAM) solution and a 10 g / L sodium bentonite (BE) suspension;

[0082] (3) Stir the algal solution sample obtained in step (1) at 200 rpm for 2 min, then at 50 rpm, add CPAM solution within 1 min to make the concentration of CPAM in the algal solution 0.5 mg / L, then stir again at 200 rpm for 2 min to make the agent evenly dispersed, then stir at 50 rpm, add BE suspension within 1 min to make the concentration of BE in the algal solution 60 mg / L, continue to stir at 200 rpm for 2 min to make the agent evenly dispersed, stir at 50 rpm for 5 min, let it settle for 10 min, pour off the supernatant, collect the settled microalgal flocs, dry and dehydrate to obtain microalgal powder.

[0083] Experimental Example 1: Characterization of Microalgae Flocculation Harvesting Effect under Algal Solution Salinity of 5‰

[0084] Following the microalgae harvesting method of Example 1, PDDAC combined with BE was used for microalgae flocculation harvesting under algal solution salinity of 5‰. PDDAC dosages were set at 0.2 mg / L and 0.4 mg / L, and BE dosages were set at 2, 4, 6, 8, 10, and 12 mg / L. Referring to the microalgae harvesting methods of Comparative Examples 1 and 2, PDDAC dosages of 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, and 2.0 mg / L, and BE dosages of 2, 4, 6, 8, 10, and 12 mg / L were used to compare the flocculation effects of different flocculant dosages.

[0085] The microalgae harvesting efficiency (HE) is calculated using the following formula:

[0086] ;

[0087] In the formula, A 0 represents the OD of the original algal solution. 685 value, A 1 represents the OD of the sample taken after sedimentation. 685 The value is the OD value of the supernatant taken after the algal solution has undergone flocculation treatment. 685 The absorbance value at that location.

[0088] Experimental results as follows Figure 1 and Figure 2 As shown.

[0089] like Figure 1 As shown, PDDAC exhibits excellent flocculation performance under salinity conditions of 5‰, with the microalgae harvest rate increasing with increasing dosage, reaching 94.6±2.0% at 0.8 mg / L. BE alone has almost no flocculation effect, with a harvest rate less than 15%. When PDDAC is combined with BE, the harvest rate continuously increases with increasing BE dosage. At a PDDAC dosage of 0.2 mg / L, the highest flocculation result is 65.2±2.7%, at which point the BE dosage is 10 mg / L. Further increases in BE dosage lead to a decrease in harvest rate. At a PDDAC dosage of 0.4 mg / L, the flocculation effect is better when combined with BE, reaching a harvest rate of 90.9±2.1% at BE dosage of 6 mg / L, and further increases in BE dosage result in a harvest rate approaching 100%. Compared to using PDDAC alone (optimal dosage of 0.8 mg / L), this method saves 50% of PDDAC usage.

[0090] like Figure 2As shown, 0.4 mg / L PDDAC had a certain flocculation effect, with a harvest rate of 76.7±2.4%. Compared with the original algal solution without flocculant, the upper algal solution after flocculation was lighter in color, a pale green. 6 mg / L BE had almost no flocculation effect, and the algal solution was similar to the original solution, a dark green. At the optimal dosage of PDDAC+BE (0.4+6 mg / L), algal cells were clearly separated from the culture medium, with algal particles settling at the bottom of the beaker. The supernatant was clear and transparent, with no obvious algal flocs. Figure 2 (Figure A) Figure 2 As shown in Figure (B), the algal cells in the original algal solution sample without flocculant were green spherical with a diameter of approximately 5 μm. The algal cells were evenly dispersed in the field of view, and observation revealed that they exhibited a certain degree of motility, indicating vigorous algal cell activity. Adding only 0.4 mg / L PDDAC to flocculate the microalgae resulted in fine, fragmented flocs with a size of approximately 170 μm. Adding only 6 mg / L BE resulted in only sporadic aggregates (approximately 30 μm in diameter) formed by a few algal cells, primarily because the BE particles had a certain adsorption capacity, attracting nearby algal cells. The corresponding dose of PDDAC combined with BE (0.4 + 6 mg / L) formed large, compact flocs with a size of approximately 380 µm.

[0091] Experimental Example 2: Characterization of Microalgae Flocculation Harvesting Effect under Algal Solution Salinity of 10‰

[0092] Following the microalgae harvesting method of Example 2, PDDAC combined with BE was used for microalgae flocculation harvesting under an algal solution salinity of 10‰. PDDAC dosages were set at 0.2 mg / L and 0.4 mg / L, and BE dosages were set at 2, 4, 6, 8, 10, and 12 mg / L. Referring to the microalgae harvesting methods of Comparative Examples 1 and 2, PDDAC dosages of 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, and 2.0 mg / L, and BE dosages of 2, 4, 6, 8, 10, and 12 mg / L were used to compare the flocculation effects of different flocculant dosages. The microalgae harvest rate was calculated using the same method as in Example 1.

[0093] Experimental results are as follows Figure 3 and Figure 4 As shown.

[0094] like Figure 3As shown, PDDAC exhibits excellent flocculation performance even at a salinity of 10‰, achieving a yield of 90% at a relatively low dose (1 mg / L), and approaching 100% with further increases in dose, indicating strong salinity tolerance of PDDAC. Adding BE alone has almost no flocculation effect, with a yield of less than 15% within the set dosage range. When PDDAC is combined with BE, the yield achieved at 0.2 mg / L PDDAC combined with BE is slightly higher than at a salinity of 5‰. At a BE dose of 12 mg / L, the yield reaches 88.0±3.2%, while the yield at 0.4 mg / L PDDAC combined with 10 mg / L BE reaches 92.1±2.6%. Compared to using PDDAC alone, the combination can save 50-75% of the PDDAC dosage.

[0095] like Figure 4 As shown, 0.4 mg / L PDDAC had a certain flocculation effect, with a harvest rate of 70.6±2.4%, and the supernatant after sedimentation was light green. After flocculation and sedimentation with 10 mg / L BE, the algal solution was similar to the original algal solution without flocculant, being dark green, showing no flocculation effect. After flocculation and sedimentation with PDDAC+BE (0.4+10 mg / L), the algal cells settled at the bottom of the beaker, and the supernatant was clear and transparent, indicating a good flocculation effect. Figure 4 (Figure A) Figure 4 As shown in Figure (B), the algal cells in the original algal solution sample without flocculant were uniformly dispersed in the field of view and exhibited some motility. Adding only 0.4 mg / L PDDAC to flocculate the microalgae resulted in fine, fragmented flocs with a size of approximately 90 μm. Adding only 10 mg / L BE resulted in sporadic small aggregates of several cells, with a diameter of approximately 30 μm. The corresponding dose of PDDAC combined with BE (0.4 + 10 mg / L) formed large, compact flocs with a size of approximately 410 µm.

[0096] Experimental Example 3: Characterization of Microalgae Flocculation Harvesting Effect under Algal Solution Salinity of 20‰

[0097] Following the microalgae harvesting method of Example 3, PDDAC combined with BE was used for microalgae flocculation harvesting under an algal solution salinity of 20‰. PDDAC dosages were set at 0.5 mg / L and 1 mg / L, and BE dosages were set at 2, 4, 6, 8, 10, and 12 mg / L. Referring to the microalgae harvesting methods of Comparative Examples 1 and 2, PDDAC dosages of 0.5, 1, 2, 6, 20, 50, 60, 70, 80, 90, and 100 mg / L, and BE dosages of 2, 4, 6, 8, 10, and 12 mg / L were used to compare the flocculation effects of different flocculant dosages. The microalgae harvest rate was calculated using the same method as in Example 1.

[0098] Experimental results are as follows Figure 5 and Figure 6 As shown.

[0099] like Figure 5 As shown, under a salinity of 20‰, the flocculation performance of PDDAC was significantly inhibited, with a harvest rate of only 73.9±2.7% at 100 mg / L. Adding BE alone had almost no flocculation effect, with a harvest rate of less than 20% within the set dosage range. When PDDAC was combined with BE, ideal harvesting results were achieved at both PDDAC dosages of 0.5 mg / L and 1 mg / L. Specifically, 0.5 mg / L PDDAC combined with 10 mg / L BE achieved a harvest rate of 91.0±1.4%, while 1 mg / L PDDAC combined with 6 mg / L BE achieved a harvest rate of 92.7±1.2%.

[0100] like Figure 6 As shown, after flocculating microalgae with 0.5 mg / L PDDAC and 10 mg / L BE respectively, the algal solution remained dark green, not much different from the original algal solution without flocculant. However, after flocculating microalgae with a mixture of PDDAC and BE at the corresponding dosages (0.5 + 10 mg / L), the algal cells settled at the bottom of the beaker, and the supernatant was colorless and clear. Figure 6 (Figure A). The algal cells in the original algal solution sample without flocculant were uniformly dispersed in the field of view and exhibited some motility. Adding only 0.5 mg / L PDDAC and only 10 mg / L BE resulted in only a few cells aggregating into very small aggregates, approximately 20 μm in diameter. PDDAC struggles to form effective flocs at higher salinity levels, primarily because the positive charge of PDDAC is weakened under medium-to-high salinity conditions, inhibiting charge neutralization with microalgal cells and hindering effective floc formation. The corresponding doses of PDDAC combined with BE (0.5 + 10 mg / L) formed large and compact flocs, with a floc size of approximately 560 µm.

[0101] Experiment Example 4: Characterization of Microalgae Flocculation Harvesting Effect under Algal Solution Salinity of 30‰

[0102] Following the microalgae harvesting method of Example 4, PDDAC combined with BE was used for microalgae flocculation harvesting under an algal solution salinity of 30‰. PDDAC dosages were set at 0.5 mg / L and 1 mg / L, and BE dosages were set at 10, 20, 30, 40, 50, and 60 mg / L. Referring to the microalgae harvesting methods of Comparative Examples 1 and 2, PDDAC dosages of 0.5, 1, 2, 6, 20, 50, 60, 70, 80, 90, and 100 mg / L, and BE dosages of 10, 20, 30, 40, 50, and 60 mg / L were used to compare the flocculation effects of different flocculant dosages. The microalgae harvest rate was calculated using the same method as in Example 1.

[0103] Experimental results are as follows Figure 7 and Figure 8 As shown.

[0104] like Figure 7 As shown, the harvest of PDDAC increased slowly with increasing dosage, reaching 50.5 ± 3.4% at 80 mg / L. BE exhibited certain flocculation ability at this salinity, achieving a harvest of 40.7 ± 2.8% at 50 mg / L. This is because the high ionic strength compresses the electric double layer thickness, increasing the collision probability between BE particles and algal cells, and promoting the aggregation of BE particles into algal cells to form larger flocs. Therefore, BE, as a loading agent, can play a more significant role in the flocculation of high-salt systems. When PDDAC was combined with BE, both dosages achieved ideal harvesting results: 0.5 mg / L PDDAC combined with 30 mg / L BE yielded a harvest of 95.7 ± 1.4%, and 1 mg / L PDDAC combined with 40 mg / L BE yielded a harvest of 91.7 ± 1.3%.

[0105] like Figure 8 As shown, after flocculating microalgae with 0.5 mg / L PDDAC, the algal solution remained dark green, not significantly different from the original algal solution without flocculant. When the BE dosage was 30 mg / L, the supernatant of the flocculated algal solution was green, slightly lighter than the original algal solution without flocculant, with a harvest rate of 28.6 ± 2.0%. After flocculating microalgae with a combination of PDDAC and BE at corresponding dosages (0.5 + 30 mg / L), the algal cells settled at the bottom of the beaker, and the supernatant was clear and transparent. Figure 8 (Figure A) Figure 8As shown in Figure (B), the algal cells in the original algal solution sample without flocculant were uniformly dispersed in the field of view and exhibited some motility. Adding only 0.5 mg / L PDDAC resulted in almost no floc formation after flocculation of the microalgae. Adding only 30 mg / L BE resulted in the formation of fine, fragmented flocs with a size of approximately 70 μm, indicating that high salinity conditions favored the adsorption effect of BE and promoted the formation of microalgal flocs. The corresponding dosage of PDDAC combined with BE (0.5 + 30 mg / L) formed large and compact flocs with a size of approximately 450 µm.

[0106] Experimental Example 5: Characterization of Microalgae Flocculation Harvesting Effect under Algal Solution Salinity of 40‰

[0107] Following the microalgae harvesting method of Example 5, PDDAC combined with BE was used for microalgae flocculation harvesting under an algal solution salinity of 40‰. PDDAC dosages were set at 0.5 mg / L and 1 mg / L, and BE dosages were set at 30, 40, 50, 60, 70, and 80 mg / L. Referring to the microalgae harvesting methods of Comparative Examples 1 and 2, PDDAC dosages of 0.5, 1, 2, 6, 20, 50, 60, 70, 80, 90, and 100 mg / L, and BE dosages of 30, 40, 50, 60, 70, and 80 mg / L were used to compare the flocculation effects of different flocculant dosages. The microalgae harvest rate was calculated using the same method as in Example 1.

[0108] Experimental results are as follows Figure 9 and Figure 10 As shown.

[0109] like Figure 9 As shown, the PDDAC harvest rate curve showed no significant upward trend within the 0-100 mg / L dosage range, indicating that further increasing the dosage would not effectively improve the harvest. At a dosage of 100 mg / L, the achievable harvest rate of PDDAC was only 13.8 ± 1.5%. Combining the microalgae harvest data under salinities of 5‰, 10‰, 20‰, and 30‰, it can be found that the flocculation performance of the cationic polymer PDDAC is affected by environmental salinity. Under high salinity conditions, BE exhibited certain flocculation ability, with the harvest rate increasing with increasing BE dosage, reaching 52.0 ± 3.0% at 80 mg / L. When PDDAC is combined with BE, a yield of over 90% can be achieved when 0.5 mg / L PDDAC is combined with 60-80 mg / L BE. However, when PDDAC is combined with BE at 1 mg / L, the yield initially increases with the increase of BE dosage, reaching 82.1±2.5% at 60 mg / L. After that, the yield decreases slightly with further increases in BE, failing to reach 90%. This indicates that the dosage of PDDAC should not be excessive when combined with BE.

[0110] like Figure 10 As shown, after flocculation with 0.5 mg / L PDDAC, the algal solution remained dark green, not significantly different from the original algal solution without flocculant. When the BE dosage was 60 mg / L, the supernatant of the flocculated algal solution was green, slightly lighter in color than the original algal solution without flocculant, with a harvest rate of 38.3 ± 3.2%. After flocculating the microalgae with a combination of PDDAC and BE at corresponding dosages (0.5 + 60 mg / L), the algal cells settled at the bottom of the beaker, and the supernatant was colorless and clear. Figure 10 (Figure A). The sedimentation effects of PDDAC alone, BE alone, and PDDAC combined with BE after flocculation of microalgae indicate that the excellent microalgae flocculation performance comes from the synergistic effect of PDDAC and BE, rather than the simple sum of the flocculation effects of PDDAC and BE. Figure 10 As shown in Figure (B), the algal cells in the original algal solution sample without flocculant were uniformly dispersed in the field of view and exhibited some motility. Adding only 0.5 mg / L PDDAC to flocculate the microalgae resulted in almost no floc formation. Adding only 30 mg / L BE to flocculate the microalgae resulted in fine, fragmented flocs with a size of approximately 120 μm. The corresponding dose of PDDAC combined with BE (0.5 + 60 mg / L) formed larger flocs with a size of approximately 380 µm. It is generally believed that larger, more compact flocs are more likely to settle under gravity, leading to better harvesting results. At salinities of 5‰-40‰, PDDAC+BE flocculation of the microalgae resulted in larger flocs, which is beneficial for the sedimentation of algal cell aggregates in high-density culture media.

[0111] Experimental Example 6: Effect of different feeding sequences on microalgae flocculation harvest rate

[0112] Under salinity conditions of 5‰-40‰, the microalgae harvesting rate was determined by comparing the microalgae harvesting methods of Example 1 and Comparative Example 3. Specifically, the dosages of PDDAC and BE were 0.4 and 6 mg / L at 5‰ salinity, 0.4 and 10 mg / L at 10‰ salinity, 0.5 and 10 mg / L at 20‰ salinity, 0.5 and 30 mg / L at 30‰ salinity, and 0.5 and 60 mg / L at 40‰ salinity. The microalgae harvesting rate was calculated using the same method as in Example 1.

[0113] Experimental results are as follows Figure 11 As shown.

[0114] Under five salinity conditions, the method used in Example 1, which involved adding PDDAC first and then BE, achieved a harvest rate of over 90%. In contrast, the harvest rates of Comparative Example 3, which involved adding BE first and then PDDAC, were 76.4±1.3%, 77.3±1.2%, 74.1±1.22%, 63.1±1.9%, and 70.1±1.3% respectively under the five salinity conditions, significantly lower than those of Example 1. The results indicate that when harvesting microalgae using PDDAC combined with BE, the first-added PDDAC primarily neutralizes the negative charge on the microalgae surface through charge neutralization, altering the stability of the algal solution system. The subsequently added BE, however, provides better adsorption, double-layer compression, and co-sedimentation effects, resulting in better flocculation and harvesting performance.

[0115] Experimental Example 7: Comparison of the effects of different cationic polymers combined with BE to flocculate microalgae

[0116] Under high salinity conditions (30‰ and 40‰), the harvesting method of Comparative Example 4 was used to harvest microalgae using a combination of CPAM and BE. The experimental results are as follows: Figure 13 As shown.

[0117] The results showed that under both salinity conditions, the harvest rate increased slowly with increasing BE dosage, but within the set BE dosage range, the harvest rate reached 90%. The maximum harvest rates achievable at salinity of 30‰ and 40‰ were 36.3±1.3% and 56.8±3.3%, respectively, at which the CPAM+BE dosages were 0.5+60 mg / L and 0.5+80 mg / L. Compared with BE flocculation alone, the improvement in harvest rate achieved by CPAM combined with BE was minimal. Under high salinity conditions, the harvest rate achieved by CPAM combined with BE was mainly due to the contribution of BE alone. In contrast, the PDDAC combined with BE used in the example achieved a harvest rate of over 90%. The ideal flocculation efficiency came from the synergistic effect of PDDAC and BE, significantly better than Comparative Example 4.

[0118] Experimental Example 8: Characterization of floc microstructure, shear resistance and recovery ability

[0119] Methods for characterizing the microstructure of flocs:

[0120] Take appropriate amounts of the original microalgal solution and the flocculent suspension from the bottom of the beaker after flocculation and sedimentation, and drop them onto the center of a clean glass slide. Gently cover with a coverslip to prepare specimens. Observe the morphology of microalgal cells and the aggregation of microalgal flocs under a microscope (XSP-63B, Shanghai No. 1 Optical Instrument Factory). Measure the size of the flocs using a scale (length from one edge of the floc to the other edge, selecting at least three fields of view). Take pictures using a digital imaging system and record the experimental results.

[0121] Methods for characterizing shear resistance and recovery:

[0122] To study the formation process and structural stability of flocs, a rapid stirring was set up based on the coagulation experimental procedure to simulate high external shear force. The floc breakage and re-flocculation were observed, and the floc size was measured by microscope. The specific experimental procedure is as follows: (1) After the flocculation procedure was completed and the chemical was added, the rotation speed was set to 50 rpm for 5 min. This is the floc growth stage. After 5 min, the suspended flocs were taken to prepare a specimen slide, and the floc size was measured by microscope. d 1); (2) Adjust the rotation speed to 350 for 5 minutes. This is the floc breaking stage. After 5 minutes, collect the suspended flocs and measure the floc size. d 2); (3) Adjust the rotation speed to 50 rpm and continue for 5 min. This is the floc re-flocculation stage. After 5 min, collect the suspended flocs and measure the floc size. d 3). By measuring the floc size at three stages, the strength factor (SF) and recovery factor (RF) of the flocs are calculated to quantify their shear resistance and recovery capacity. The calculation formulas are shown below:

[0123] ;

[0124] ;

[0125] in, d 1. d 2. d 3 represents the average size (µm) of the flocs at the end of the three stages.

[0126] Experimental results are as follows Figure 13 As shown.

[0127] The particle size distribution, shear resistance, resilience, and structural characteristics of flocs determine their settling performance, yield, and the stability of the harvesting process during solid-liquid separation. Rapid stirring of microalgal flocs can simulate external disturbances; the looser the flocs, the smaller their size after stirring, and the more compact they are, the stronger their resistance to external disturbances and the better they can maintain a larger size.

[0128] Floc sizes formed by 0.8 mg / L PDDAC at 5‰ salinity and 1 mg / L PDDAC at 10‰ salinity ( d 1) The flocs were 283±12 µm and 260±10 µm respectively. After rapid stirring and shearing, the flocs became smaller, and their size ( d 2) The flocs were 103±6 µm and 83±6 µm respectively. After stopping rapid stirring and switching to slow stirring, the broken flocs flocculated again, eventually forming flocs of 263±6 µm and 177±12 µm. d3) Floc size. At salinities of 5‰ and 10‰, the floc strength factor (SF) was 36.4±3.6% and 34.8±2.2%, respectively, and the recovery factor (RF) was 88.8±4.8% and 56.0±3.0%, respectively. The final harvest rates after settling were 92.3±1.8% and 92.0±1.4%, respectively. This indicates that under low salinity conditions, the flocs formed by PDDAC have good recovery ability, strong anti-interference ability, and high harvest efficiency after re-flocculation. When the microalgal salinity was 5‰, 10‰, 20‰, 30‰, and 40‰, the optimal dosages of PDDAC and BE (see the diagram of optimal dosage ratio and sedimentation effect) were as follows: Figure 14 As shown) the size of the flocs formed ( d 1) The floc sizes were 373±6, 403±15, 560±10, 447±6 and 378±15 µm, respectively. After rapid mixing and crushing, the floc sizes were ( d 2) After the flocs decreased to 130±10 µm, 137±6 µm, 127±6 µm, 136±6 µm and 143±6 µm, and after slow stirring was resumed, the flocs recovered to grow to 313±6 µm, 343±6 µm, 487±12 µm, 380±10 µm and 227±15 µm. d 3) The intensity factors SF were 34.8±2.2%, 33.9±1.0%, 22.6±0.7%, 30.0±0.9% and 38.1±1.1%, respectively, and the recovery factors RF were 75.3±0.6%, 77.5±2.9%, 83.0±1.5%, 78.5±1.9% and 35.7±3.3%, respectively.

[0129] Compared to PDDAC, PDDAC combined with BE can form larger flocs at low, medium and high salinity. Even after crushing, the size of the flocs remains large, and the flocs can quickly recover and grow to a larger size after external disturbance is stopped. This allows it to achieve a high harvest rate after final settling (harvest rates of 90.5±0.8%, 91.5±1.5%, 90.4±1.4%, 85.6±1.4% and 81.3±1.0% at the five salinity levels, respectively). Overall, as salinity increased, the floc size gradually decreased during the initial stabilization period, indicating that salinity affects the interaction between the flocculant and microalgal cells, thus affecting the formation of large-sized flocs. After rapid agitation and crushing, the floc size formed by PDDAC alone was 80-100 µm, while that formed by the compound group was between 120-140 µm. The floc size of the compound group after crushing was significantly higher than that of the PDDAC-only group. In the final stabilization stage, the floc size formed by the PDDAC-only group was between 170-260 µm. Except for the relatively small flocs formed by the PDDAC-BE compound at 40‰ salinity, the floc size was between 310-490 µm at 5‰-30‰ salinity, showing excellent reflocculation ability. This allows the PDDAC-BE compound to maintain excellent flocculation performance in higher salinity environments and achieve ideal sedimentation results.

[0130] 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 harvesting wide salinity microalgae by cationic polymer complexed bentonite flocculation, characterized in that, The cationic polymer is polydiallylammonium chloride, and the bentonite is sodium bentonite. The salinity range of the wide salinity is 5‰-40‰; Includes the following steps: Based on the biomass of the microalgae cells to be harvested, add polydiallyl ammonium chloride solution and sodium bentonite suspension to the algal solution, stir, collect by sedimentation, and complete the harvest. In this process, after adding polydiallylammonium chloride solution, stir for 1-5 minutes and then add sodium bentonite suspension. The total concentration of polydimethyldiallylammonium chloride in the algal solution was 0.4, 0.5, or 1 mg / L, and the total concentration of sodium bentonite in the algal solution was 6, 10, 30, or 60 mg / L.

2. The method for harvesting wide-salinity microalgae by flocculation of cationic polymer compounded with bentonite according to claim 1, characterized in that, The settling time is 5-15 minutes.

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