Application and harvesting method for harvesting wide-salinity microalgae through cationic polymer compounded bentonite flocculation

Abstract

The invention discloses application of cationic polymer compounded bentonite flocculation for harvesting wide-salinity microalgae and a harvesting method, and belongs to the technical field of environmental protection. The method comprises the following steps: adding a polydimethyldiallylammonium chloride solution and a sodium bentonite suspension into an algae solution according to the cell biomass of microalgae to be harvested, stirring, settling and collecting to finish harvesting. According to the method disclosed by the invention, the microalgae in the wide-salt environment are harvested by combining PDDAC and BE for flocculation, the microalgae can be efficiently flocculated and harvested within the range of 0-40% of water salinity, and the harvesting rate can reach 90% or above; the flocculating efficiency is high, the dosage of a flocculating agent is small, the floc is large in size and compact, and the salt-resistant characteristic is remarkable; the method is suitable for efficient harvesting of microalgae in artificial culture or natural water under a wide salinity condition, provides a key technology for the field of microalgae harvesting, and has a wide application prospect; the problems of poor salinity tolerance of a flocculating agent, large dosage of the flocculating agent and poor harvesting effect in microalgae harvesting through flocculation at present are solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of environmental protection, and particularly relates to application of a cationic polymer compound bentonite flocculation and a method for collecting microalgae with wide salinity. BACKGROUND

[0002] Microalgae are considered as primary producers in water bodies, and have high photosynthetic efficiency and fast growth rate. Microalgae have strong environmental adaptability and are widely distributed in fresh water, 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‰), and have the dual nature of resources and pollution. Microalgae have 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 surface (-10--35 mV), and can be stably dispersed in algal liquid. From the perspectives of environmental governance and resource utilization, microalgae need to be efficiently separated from water. Compared with natural sedimentation, mechanical salvage, membrane separation and centrifugation, flocculation is concerned due to the advantages of simple operation, low cost, rapidness, high efficiency and easy combination with other methods. Flocculation is to make algal cells aggregate and become large through charge neutralization, adsorption bridging, net capture and sweeping between flocculants and algal cells, and then form flocs to achieve the effect of algal water separation. Traditional flocculants mainly include inorganic flocculants (such as iron salts and aluminum salts) and organic polymer flocculants (such as polyacrylamide CPAM), but they are usually not suitable for flocculation of microalgae in medium and high salinity water bodies. The main reasons are as follows: on the one hand, the high ion strength in salt water environment will shield the charged sites of flocculants and microalgae, and inhibit the charge neutralization between them; on the other hand, the high ion strength will reduce the repulsion force in the polymer, causing the molecular curling of the polymer flocculant, and then weakening the adsorption bridging effect. Therefore, it is urgent to develop a wide-salinity-tolerant and efficient microalgae flocculation reagent and method.

[0003] The complex flocculation can comprehensively utilize the performance of various single flocculants, effectively compensate for the shortcomings of single flocculants, and achieve synergistic effect. For example, the combination of organic flocculants and inorganic flocculants: Pan et al. proposed that the combination of amphoteric starch and polyaluminum chloride can achieve high-efficiency flocculation and harvesting of microalgae in a wide salt range. Loading flocculation: the combination of flocculants and loading agents (insoluble solid particles as loading agents) can accelerate the formation and precipitation of flocculation by using the gravity settling property or magnetic property and adsorption of loading agents, including micro-sand and magnetic loading flocculation. Micro-particle flocculation: the micro-particle retention system in the wet part of papermaking can also be considered as a special flocculation system. Unlike loading flocculation, the gravity settling property of the micro-particle component is not high, and is often determined by the interaction between the pre-floc formed by the flocculant and the pulp slurry and the micro-particles. The synergistic effect of different flocculants, micro-particles, and flocculation objects is quite different. For example, in the wet part of papermaking, CPAM is often combined with bentonite (BE), and cationic starch is combined with nano-silica sol. Moreover, the structure of the flocculants and micro-particles has a high requirement.

[0004] However, the flocculation efficiency of the cationic polymer (such as CPAM) used in the complex flocculant depends on the bridging effect of the super-molecular weight (about 8-15 million). In a high-salinity environment, the CPAM molecular chain is curled too much due to the high ionic strength, which greatly weakens the bridging effect. A small amount of cationic groups loses the charge shielding and cannot charge, which makes it difficult to meet the harvesting requirements in a high-salinity environment. Therefore, a method for harvesting microalgae in different salinity conditions, including high-salinity conditions, is urgently needed. SUMMARY

[0005] To solve the above technical problems, the purpose of the present application is to provide a cationic polymer complex bentonite flocculation method for harvesting microalgae in a wide salinity range, so as to solve the problem that the existing complex flocculant for harvesting microalgae has poor harvesting effect in a high-salinity environment and cannot achieve high-efficiency flocculation harvesting in a wide salinity range.

[0006] The technical solution of the present application to solve the above technical problems is as follows: In a first aspect, the present application provides a cationic polymer complex bentonite flocculation method for harvesting microalgae in a wide salinity range. The cationic polymer is polydimethyl diallyl ammonium chloride, and the bentonite is sodium-based bentonite.

[0007] Further, the dosage of polydimethyl diallyl ammonium chloride used in the flocculation and harvesting of microalgae 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.

[0008] In a second aspect of the present application, a method for harvesting wide-salinity microalgae by cationic polymer and bentonite flocculation is provided, comprising the following steps: According to the biomass of the microalgae cells to be harvested, a solution of polydimethyl diallyl ammonium chloride and a suspension of sodium-based bentonite are added and stirred, and then collected by sedimentation to complete the harvesting.

[0009] Further, the biomass of the microalgae cells is determined by the following method: A certain volume of the microalgae sample is filtered through a microporous filter membrane with a pore size of 0.45 μm. The filter membrane is dried to a constant weight before and after filtration and weighed. After filtration, the filter membrane is placed in an oven and dried to a constant weight and weighed. The difference between the two weights is divided by the filtration volume to obtain the concentration of the microalgae cell biomass (g / L). The determination is repeated three times, and the average value is taken. Then, the biomass of the microalgae cells is calculated according to the volume of the algal liquid to be harvested.

[0010] Further, the concentration of the solution of polydimethyl diallyl ammonium chloride is 1-2 g / L, and the concentration of the suspension of sodium-based bentonite is 5-15 g / L.

[0011] Further, the amount of polydimethyl diallyl ammonium 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.

[0012] Further, the solution of polydimethyl diallyl ammonium chloride is added first, and then the suspension of sodium-based bentonite is added.

[0013] Further, after adding the solution of polydimethyl diallyl ammonium chloride, the solution is stirred for 1-5 min, and then the suspension of sodium-based bentonite is added.

[0014] Further, before adding the solution of polydimethyl diallyl ammonium chloride, the algal liquid is stirred at 150-250 rpm for 1-3 min, and then stirred at 40-60 rpm. After adding the solution of polydimethyl diallyl ammonium chloride within 30-90 s, the algal liquid is stirred at 150-250 rpm for 1-3 min to disperse the medicament uniformly, and then stirred at 40-60 rpm. The suspension of sodium-based bentonite is added within 30-90 s. The algal liquid is first stirred at 150-250 rpm for 1-3 min to disperse the medicament uniformly, and then stirred at 40-60 rpm for 1-10 min. Then, the stirring is stopped for sedimentation.

[0015] Further, the time for sedimentation is 5-15 min.

[0016] The present application has the following beneficial effects: The present application provides a method for flocculating and harvesting microalgae under wide salt conditions by combining polydimethyl diallyl ammonium chloride (PDDAC) with sodium bentonite (BE), which can achieve efficient flocculation and harvesting of microalgae in a water body with a salinity of 0‰ to 40‰, and the harvesting rate can reach more than 90%. The method has high flocculation efficiency, low flocculant dosage, large and compact flocculation size, and significant salt resistance; the method is suitable for efficient harvesting of microalgae in artificial breeding or natural water bodies under wide salinity conditions, provides key technology for the microalgae harvesting field, and has wide application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Figure 5 is a graph of the change of the harvesting rate of microalgae with the dosage of PDDAC, BE and PDDAC compounded BE under 5‰ salinity conditions, wherein (A) is PDDAC alone, (B) is BE alone, and (C) is PDDAC compounded BE; Figure 2 Figure 6 is a graph of the settling effect and micro-morphology of the flocculated microalgae under 5‰ salinity conditions, wherein (A) is the settling effect graph, and (B) is the micro-morphology graph; Figure 3 Figure 10 is a graph of the change of the harvesting rate of microalgae with the dosage of PDDAC, BE and PDDAC compounded BE under 10‰ salinity conditions, wherein (A) is PDDAC alone, (B) is BE alone, and (C) is PDDAC compounded BE; Figure 4 Figure 11 is a graph of the settling effect and micro-morphology of the flocculated microalgae under 10‰ salinity conditions, wherein (A) is the settling effect graph, and (B) is the micro-morphology graph; Figure 5 Figure 15 is a graph of the change of the harvesting rate of microalgae with the dosage of PDDAC, BE and PDDAC compounded BE under 20‰ salinity conditions, wherein (A) is PDDAC alone, (B) is BE alone, and (C) is PDDAC compounded BE; Figure 6 Figure 16 is a graph of the settling effect and micro-morphology of the flocculated microalgae under 20‰ salinity conditions, wherein (A) is the settling effect graph, and (B) is the micro-morphology graph; Figure 7 Figure 20 is a graph of the change of the harvesting rate of microalgae with the dosage of PDDAC, BE and PDDAC compounded BE under 30‰ salinity conditions, wherein (A) is PDDAC alone, (B) is BE alone, and (C) is PDDAC compounded BE; Figure 8 Figure 21 is a graph of the settling effect and micro-morphology of the flocculated microalgae under 30‰ salinity conditions, wherein (A) is the settling effect graph, and (B) is the micro-morphology graph; Figure 9Figure 4 is a graph of the harvest rate of microalgae flocculated by PDDAC, BE and PDDAC compounded BE under the condition of 40‰ salinity, wherein (A) is PDDAC alone, (B) is BE alone, and (C) is PDDAC compounded BE; Figure 10 Figure 5 is a graph of the settling effect of microalgae flocculated under the condition of 40‰ salinity and a microstructure morphology diagram of the formed flocs, wherein (A) is a settling effect diagram, and (B) is a microstructure morphology diagram; Figure 11 Figure 6 is a comparison diagram of the harvest rate of the harvesting method of Example (PDDAC+BE) and Comparative Example 3 (BE+PDDAC) under different salinity conditions; Figure 12 Figure 7 is a graph of the harvest rate of microalgae harvested by CPAM compounded BE, wherein (A) is under the condition of 30‰ salinity, and (B) is under the condition of 40‰ salinity; Figure 13 Figure 8 is a diagram of the floc size, strength factor and recovery factor of the flocs formed by PDDAC alone and PDDAC compounded BE flocculating microalgae, wherein (A) is PDDAC alone, and (B) is PDDAC+BE; Figure 14 Figure 9 is a diagram of the optimal dosage and settling effect of PDDAC compounded BE for harvesting microalgae under the conditions of 5‰-40‰ salinity. DETAILED DESCRIPTION

[0018] The principles and characteristics of the present application are described below in conjunction with the accompanying drawings, and the examples are only used to explain the present application and are not intended to limit the scope of the present application. If no specific conditions are specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If no manufacturer of the reagents or instruments used is specified, they are all conventional products that can be purchased on the market.

[0019] The main drugs used in the examples are as follows: Cationic polyacrylamide with a molecular weight of 8-10 million and an ionic degree of 30-35% (Shanghai Maikelin Biochemical Technology Co., Ltd.); polydimethyl diallyl ammonium chloride with a molecular weight of 200,000 and a concentration of 20% (Shanghai Aladdin Biochemical Technology Co., Ltd.); sodium bentonite (analytical pure, Tianjin Huasheng Chemical Reagent Co., Ltd.); the experimental microalgae is Chlorella vulgaris (Chlorella vulgaris) Chlorella vulgaris ), purchased from Yangzhou Shanze Biological Technology Co., Ltd., and the basic properties of the microalgae are as follows: OD 685 (685 nm wavelength absorbance) is 1.500±0.003, pH is 7.0±0.3, salinity is 5.0±0.1‰, and algal cell biomass is 0.975±0.058 g / L. The salinity of the algal liquid is adjusted by adding sodium chloride to obtain microalgae samples with different salinities while ensuring that the other basic properties of the microalgae samples remain unchanged.

[0020] Example 1 A method for harvesting microalgae by using cationic polymer compounded bentonite under the condition of 5‰ salinity of algal liquid, comprising the following steps: (1) Adjust the salinity of the algal liquid to be harvested to 5‰ by adding sodium chloride as the algal liquid sample to be harvested in this example; (2) Prepare a polydimethyl diallyl ammonium chloride (PPDAC) solution with a concentration of 1.5 g / L and a sodium-based bentonite (BE) suspension with a concentration of 10 g / L; (3) Stir the algal liquid sample obtained in step (1) at a speed of 200 rpm for 2 min, then stir at a speed of 50 rpm, and add the PPDAC solution within 1 min to make the concentration of PPDAC in the algal liquid 0.4 mg / L, then stir again at a speed of 200 rpm for 2 min to make the reagent evenly dispersed, then stir at a speed of 50 rpm, and add the BE suspension within 1 min to make the concentration of BE in the algal liquid 6 mg / L, continue to stir at a speed of 200 rpm for 2 min to make the reagent evenly dispersed, and stir at a speed of 50 rpm for 5 min, then settle for 10 min, pour the supernatant, collect the settled microalgae floc, and obtain microalgae powder after drying and dehydration.

[0021] Example 2 A method for harvesting microalgae by using cationic polymer compounded bentonite under the condition of 10‰ salinity of algal liquid, comprising the following steps: (1) Adjust the salinity of the algal liquid to be harvested to 10‰ by adding sodium chloride as the algal liquid sample to be harvested in this example; (2) Prepare a polydimethyl diallyl ammonium chloride (PPDAC) solution with a concentration of 1.5 g / L and a sodium-based bentonite (BE) suspension with a concentration of 10 g / L; (3) Stir the algal liquid sample obtained in step (1) at a speed of 200 rpm for 2 min, then stir at a speed of 50 rpm, and add the PPDAC solution within 1 min to make the concentration of PPDAC in the algal liquid 0.4 mg / L, then stir again at a speed of 200 rpm for 2 min to make the reagent evenly dispersed, then stir at a speed of 50 rpm, and add the BE suspension within 1 min to make the concentration of BE in the algal liquid 10 mg / L, continue to stir at a speed of 200 rpm for 2 min to make the reagent evenly dispersed, and stir at a speed of 50 rpm for 5 min, then settle for 10 min, pour the supernatant, collect the settled microalgae floc, and obtain microalgae powder after drying and dehydration.

[0022] Example 3 A method for harvesting microalgae by using cationic polymer compounded bentonite under the condition of 20‰ salinity of algal liquid, comprising the following steps: (1) The salinity of the algal liquid to be harvested was adjusted to 20‰ by adding sodium chloride as the algal liquid sample to be harvested in this example; (2) A solution of polydimethyl diallyl ammonium chloride (PPDAC) with a concentration of 1.5 g / L and a suspension of sodium-based bentonite (BE) with a concentration of 10 g / L were prepared; (3) The algal liquid sample obtained in step (1) was first stirred at a speed of 200 rpm for 2 min, then stirred at a speed of 50 rpm, and PPDAC solution was added within 1 min to make the concentration of PPDAC in the algal liquid 0.5 mg / L, then stirred again at a speed of 200 rpm for 2 min to make the dispersant uniform, then stirred at a speed of 50 rpm, and BE suspension was added within 1 min to make the concentration of BE in the algal liquid 10 mg / L, and then stirred at a speed of 200 rpm for 2 min to make the dispersant uniform, and then stirred at a speed of 50 rpm for 5 min, and then settled for 10 min, and then the supernatant was poured out, and then the settled microalgae floc was collected, and then dried and dehydrated to obtain microalgae powder.

[0023] Example 4: A method for harvesting microalgae under the condition of 30‰ salinity of algal liquid by using a cationic polymer compounded bentonite, comprising the following steps: (1) The salinity of the algal liquid to be harvested was adjusted to 30‰ by adding sodium chloride as the algal liquid sample to be harvested in this example; (2) A solution of polydimethyl diallyl ammonium chloride (PPDAC) with a concentration of 1.5 g / L and a suspension of sodium-based bentonite (BE) with a concentration of 10 g / L were prepared; (3) The algal liquid sample obtained in step (1) was first stirred at a speed of 200 rpm for 2 min, then stirred at a speed of 50 rpm, and PPDAC solution was added within 1 min to make the concentration of PPDAC in the algal liquid 0.5 mg / L, then stirred again at a speed of 200 rpm for 2 min to make the dispersant uniform, then stirred at a speed of 50 rpm, and BE suspension was added within 1 min to make the concentration of BE in the algal liquid 30 mg / L, and then stirred at a speed of 200 rpm for 2 min to make the dispersant uniform, and then stirred at a speed of 50 rpm for 5 min, and then settled for 10 min, and then the supernatant was poured out, and then the settled microalgae floc was collected, and then dried and dehydrated to obtain microalgae powder.

[0024] Example 5: A method for harvesting microalgae under the condition of 40‰ salinity of algal liquid by using a cationic polymer compounded bentonite, comprising the following steps: (1) The salinity of the algal liquid to be harvested was adjusted to 40‰ by adding sodium chloride as the algal liquid sample to be harvested in this example; (2) Prepare a 1.5 g / L solution of polydimethyl diallyl ammonium chloride (PPDAC) and a 10 g / L suspension of sodium bentonite (BE); (3) The algal liquid sample obtained in step (1) is first stirred at a speed of 200 rpm for 2 min, then stirred at a speed of 50 rpm, and the PPDAC solution is added within 1 min to make the concentration of PPDAC in the algal liquid 0.5 mg / L, and then stirred again at a speed of 200 rpm for 2 min to disperse the medicament uniformly; then stirred at a speed of 50 rpm, and the BE suspension is added within 1 min to make the concentration of BE in the algal liquid 60 mg / L, and then stirred at a speed of 200 rpm for 2 min to disperse the medicament uniformly, and finally stirred at a speed of 50 rpm for 5 min, then settled for 10 min, poured the supernatant, collected the settled microalgae floc, and obtained microalgae powder after drying and dehydration.

[0025] Comparative Example 1: A method for collecting microalgae under the condition of PDDAC alone at a salinity of 5‰ of algal liquid, comprising the following steps: (1) Adjust the salinity of the algal liquid to be harvested to 5‰ by adding sodium chloride as the algal liquid sample to be harvested in this example; (2) Prepare a 1.5 g / L solution of polydimethyl diallyl ammonium chloride (PPDAC); (3) The algal liquid sample obtained in step (1) is first stirred at a speed of 200 rpm for 2 min, then stirred at a speed of 50 rpm, and the PPDAC solution is added within 1 min to make the concentration of PPDAC in the algal liquid 0.2 mg / L, and then stirred at a speed of 200 rpm for 2 min to disperse the medicament uniformly, and finally stirred at a speed of 50 rpm for 5 min, then settled for 10 min, poured the supernatant, collected the settled microalgae floc, and obtained microalgae powder after drying and dehydration.

[0026] Comparative Example 2: A method for collecting microalgae under the condition of BE alone at a salinity of 5‰ of algal liquid, comprising the following steps: (1) Adjust the salinity of the algal liquid to be harvested to 5‰ by adding sodium chloride as the algal liquid sample to be harvested in this example; (2) Prepare a 1.5 g / L solution of polydimethyl diallyl ammonium chloride (PPDAC) and a 10 g / L suspension of sodium bentonite (BE); (3) The algal liquid sample obtained in step (1) is first stirred at a speed of 200 rpm for 2 min, then stirred at a speed of 50 rpm, and the BE suspension liquid is added within 1 min to make the concentration of BE in the algal liquid 2 mg / L. The stirring is continued at a speed of 200 rpm for 2 min to disperse the medicament uniformly. After stirring at a speed of 50 rpm for 5 min, the sample is settled for 10 min. The supernatant is poured out, and the settled microalgae floc is collected. After drying and dehydration, the microalgae powder is obtained.

[0027] Comparative Example 3 A method for harvesting microalgae by using a cationic polymer compounded bentonite under the condition of 5‰ salinity of algal liquid, comprising the following steps: (1) The salinity of the algal liquid to be harvested is adjusted to 5‰ by adding sodium chloride as the algal liquid sample to be harvested in this example; (2) A solution of polydimethyl diallyl ammonium chloride (PPDAC) with a concentration of 1.5 g / L and a suspension liquid of sodium-based bentonite (BE) with a concentration of 10 g / L are prepared; (3) The algal liquid sample obtained in step (1) is first stirred at a speed of 200 rpm for 2 min, then stirred at a speed of 50 rpm, and the BE suspension liquid is added within 1 min to make the concentration of BE in the algal liquid 6 mg / L. Then, the stirring is continued at a speed of 200 rpm for 2 min to disperse the medicament uniformly. Then, the stirring is continued at a speed of 50 rpm, and the PPDAC solution is added within 1 min to make the concentration of PPDAC in the algal liquid 0.4 mg / L. The stirring is continued at a speed of 200 rpm for 2 min to disperse the medicament uniformly. After stirring at a speed of 50 rpm for 5 min, the sample is settled for 10 min. The supernatant is poured out, and the settled microalgae floc is collected. After drying and dehydration, the microalgae powder is obtained.

[0028] Comparative Example 4 A method for harvesting microalgae by using a cationic polymer compounded bentonite under the condition of 30‰ salinity of algal liquid, comprising the following steps: (1) The salinity of the algal liquid to be harvested is adjusted to 30‰ by adding sodium chloride as the algal liquid sample to be harvested in this example; (2) A solution of polyacrylamide (CPAM) with a concentration of 1.5 g / L and a suspension liquid of sodium-based bentonite (BE) with a concentration of 10 g / L are prepared; (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.

[0029] Experimental Example 1: Characterization of Microalgae Flocculation Harvesting Effect under Algal Solution Salinity of 5‰ 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.

[0030] The microalgae harvesting efficiency (HE) is calculated using the following formula: ; 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.

[0031] Experimental results as follows Figure 1 and Figure 2 As shown.

[0032] like Figure 1As 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.

[0033] like Figure 2 As 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.

[0034] Experimental Example 2: Characterization of Microalgae Flocculation Harvesting Effect under Algal Solution Salinity of 10‰ Referring to the microalgae harvesting method of Example 2, PDDAC was compounded with BE to harvest microalgae under the condition of 10‰ salinity of algal liquid. The PDDAC dosage was set to 0.2 mg / L and 0.4 mg / L, and the BE dosage was set to 2, 4, 6, 8, 10 and 12 mg / L. Referring to the microalgae harvesting methods of Comparative Example 1 and Comparative Example 2, the PPDAC dosage was set to 0.2, 0.4, 0.6, 0.8, 1.0, 1.5 and 2.0 mg / L, and the BE dosage was set to 2, 4, 6, 8, 10 and 12 mg / L to conduct flocculation effect comparison experiments of different flocculant addition amounts. The microalgae harvesting rate calculation method was the same as that of Test Example 1.

[0035] The experimental results are shown in Figure 3 and Figure 4 .

[0036] As shown in Figure 3 , the flocculation performance of PDDAC is still good under the condition of 10‰ salinity, and the harvesting rate can reach 90% at a small dosage (1 mg / L). The harvesting rate can approach 100% by continuously increasing the dosage, indicating that PDDAC has strong salinity tolerance. The addition of BE alone has almost no flocculation effect, and the harvesting rate is less than 15% within the set dosage range. When PDDAC is compounded with BE, the harvesting rate of 0.2 mg / L PDDAC compounded with BE is slightly higher than that of 5‰ salinity. When the BE dosage is 12 mg / L, the harvesting rate can reach 88.0±3.2%, and the harvesting rate of 0.4 mg / L PDDAC compounded with 10 mg / L BE can reach 92.1±2.6%. Compared with the use of PDDAC alone, the compounding can save 50-75% of the PDDAC dosage.

[0037] As shown in Figure 4 , 0.4 mg / L PDDAC has a certain flocculation effect, and the harvesting rate is 70.6±2.4%. The upper algal liquid after sedimentation is light green. The algal liquid after flocculation and sedimentation of 10 mg / L BE is similar to the original algal liquid without adding flocculant, which is dark green and has no flocculation effect. After flocculation and sedimentation of PDDAC+BE (0.4+10 mg / L), the algal cells are settled at the bottom of the beaker, and the supernatant is clear and transparent, indicating good flocculation effect Figure 4 (A) of the figure. As shown in Figure 4 (B) of the figure, the algal cells of the original algal liquid sample without adding flocculant are uniformly dispersed in the field of view and have a certain movement ability. After adding 0.4 mg / L PDDAC to flocculate microalgae, fine small flocs are formed, and the floc size is about 90 μm. After adding 10 mg / L of BE, small aggregates formed by several cells are sporadically distributed, and the diameter is about 30 μm. The corresponding dosage of PDDAC compounded with BE (0.4+10 mg / L) forms large and compact flocs, and the floc size is about 410 µm.

[0038] Test Example 3: Microalgae flocculation recovery effect characterization under the condition of algal liquid salinity 20‰ Referring to the microalgae recovery method of Example 3, PDDAC was compounded with BE to recover microalgae under the condition of algal liquid salinity 20‰. The PDDAC dosage was set to 0.5 mg / L and 1 mg / L, and the BE dosage was set to 2, 4, 6, 8, 10 and 12 mg / L. Referring to the microalgae recovery method of Comparative Example 1 and Comparative Example 2, the PPDAC dosage was set to 0.5, 1, 2, 6, 20, 50, 60, 70, 80, 90 and 100 mg / L, and the BE dosage was set to 2, 4, 6, 8, 10 and 12 mg / L to conduct flocculation effect comparison experiment of different flocculant addition amount. The microalgae recovery rate calculation method is the same as that of Test Example 1.

[0039] The experimental results are shown in Figure 5 and Figure 6 .

[0040] As shown in Figure 5 , under the condition of 20‰ salinity, the flocculation performance of PDDAC was obviously inhibited, and the recovery rate that could be reached was only 73.9±2.7% at 100 mg / L. The addition of BE alone had almost no flocculation effect, and the recovery rate was less than 20% in the set dosage range. When PDDAC was compounded with BE, the addition of BE could achieve ideal recovery effect at PDDAC dosage of 0.5 mg / L and 1 mg / L, among which 0.5 mg / L PDDAC compounded with 10 mg / L BE could achieve a recovery rate of 91.0±1.4%, and 1 mg / L PDDAC compounded with 6 mg / L BE could achieve a recovery rate of 92.7±1.2%.

[0041] As shown in Figure 6 , after 0.5 mg / L PDDAC and 10 mg / L BE flocculated microalgae respectively, the algal liquid was still dark green, with little difference from the original algal liquid without adding flocculant, while after the corresponding dosage of PDDAC and BE compound (0.5+10 mg / L) flocculated microalgae, the algal cells sank to the bottom of the beaker, and the supernatant was colorless and clear Figure 6The algae cells in the original algae liquid sample without adding flocculants are uniformly dispersed in the field of view and have a certain movement ability. The addition of only 0.5 mg / L of PDDAC and only 10 mg / L of BE can only make several cells aggregate to form small aggregates with a diameter of about 20 μm. PDDAC is difficult to form effective flocs at a higher salinity, and the main reason is that the positive charge of PDDAC is weakened in a medium-high salinity environment, and the charge neutralization between PDDAC and microalgae cells is inhibited, making it difficult to form effective flocs. The corresponding dose of PDDAC compounded with BE (0.5+10 mg / L) forms large and tight flocs, and the floc size is about 560 μm.

[0042] Test Example 4: Effect of microalgae flocculation and harvesting under the condition of algae liquid salinity of 30‰ Referring to the microalgae harvesting method of Example 4, PDDAC compounded with BE was used for microalgae flocculation and harvesting under the condition of algae liquid salinity of 30‰. The PDDAC dose was set to 0.5 mg / L and 1 mg / L, and the BE dose was set to 10, 20, 30, 40, 50 and 60 mg / L. Referring to the microalgae harvesting method of Comparative Example 1 and Comparative Example 2, the PPDAC dose was set to 0.5, 1, 2, 6, 20, 50, 60, 70, 80, 90 and 100 mg / L, and the BE dose was set to 10, 20, 30, 40, 50 and 60 mg / L for flocculation effect comparison experiments of different flocculant addition amounts. The microalgae harvesting rate calculation method is the same as that of Test Example 1.

[0043] The experimental results are shown in Figure 7 and Figure 8 .

[0044] As shown in Figure 7 , the harvest of PDDAC slowly increases with the increase of the dose, and the harvest rate at 80 mg / L is 50.5±3.4%. BE shows a certain flocculation ability at this salinity, and the harvest rate reaches 40.7±2.8% at 50 mg / L. The reason is that the high ionic strength compresses the thickness of the double electric layer, which improves the collision probability between the BE particles and the algae cells, and promotes the aggregation of the BE particles to form larger flocs. Therefore, BE as a loading agent can play a more significant advantage in high-salinity flocculation. When PDDAC is compounded with BE, PDDAC compounded with BE at two doses can achieve ideal harvesting effect, of which the harvest rate of 0.5 mg / L PDDAC compounded with 30 mg / L BE is 95.7±1.4%, and the harvest rate of 1 mg / L PDDAC compounded with 40 mg / L BE is 91.7±1.3%.

[0045] As shown in Figure 8As 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 8 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 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.

[0046] Experimental Example 5: Characterization of Microalgae Flocculation Harvesting Effect under Algal Solution Salinity of 40‰ 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.

[0047] Experimental results are as follows Figure 9 and Figure 10 As shown.

[0048] like Figure 9As 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.

[0049] 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.

[0050] Experimental Example 6: Effect of different feeding sequences on microalgae flocculation harvest rate The microalgae flocculation harvesting rate determination of the microalgae harvesting method of Comparative Reference Example 1 and the microalgae harvesting method of Comparative Example 3 was carried out under the conditions of 5‰-40‰ salinity. Among them, the dosages of PDDAC and BE were 0.4 and 6 mg / L respectively at 5‰ salinity, 0.4 and 10 mg / L respectively at 10‰ salinity, 0.5 and 10 mg / L respectively at 20‰ salinity, 0.5 and 30 mg / L respectively at 30‰ salinity, and 0.5 and 60 mg / L respectively at 40‰ salinity, and the microalgae harvesting rate calculation method was the same as that of Test Example 1.

[0051] The experimental results are shown in Table 2. Figure 11

[0052] Under the conditions of five salinities, the method of adding PDDAC first and then adding BE adopted in Example 1 can achieve a harvesting rate of more than 90%, while the harvesting rate of the method of adding BE first and then adding PDDAC adopted in Comparative Example 3 under the conditions of five salinities is 76.4±1.3%, 77.3±1.2%, 74.1±1.22%, 63.1±1.9 and 70.1±1.3% in turn, which is significantly lower than that of Example 1. The results show that when PDDAC is compounded with BE to harvest microalgae, the PDDAC added first mainly neutralizes the negative charge on the surface of the microalgae through charge neutralization, changes the stability of the algal liquid system, and the BE added later can play a better adsorption, double electric layer compression and co-sedimentation effect, thereby achieving a better flocculation harvesting effect.

[0053] Test Example 7: Effect comparison of different cationic polymer compounded BE on flocculation of microalgae Under the conditions of high salinity (30‰ and 40‰), the harvesting method of Comparative Example 4 was used to harvest microalgae by compounding BE with CPAM, and the experimental results are shown in Table 4. Figure 13

[0054] The results show that under the conditions of two salinities, the harvesting rate slowly increases with the increase of the dosage of BE, but within the range of the dosage of BE set, the harvesting rate is all up to 90%, among which the maximum harvesting rates that can be achieved under the conditions of 30‰ and 40‰ salinity are 36.3±1.3% and 56.8±3.3% respectively, and at this time, the dosages of CPAM+BE are 0.5+60 mg / L and 0.5+80 mg / L respectively. By comparing the BE flocculation alone, it can be found that the CPAM compounded with BE has a very small improvement in harvesting rate, and under the conditions of high salinity, the harvesting rate achieved by the CPAM compounded with BE is basically contributed by the BE, while the PDDAC compounded with BE adopted in the example can achieve a harvesting rate of more than 90%, and the ideal flocculation efficiency comes from the synergistic effect of PDDAC and BE, which is significantly better than that of Comparative Example 4.

[0055] ​​Experimental Example 8: Characterization of floc microstructure, shear resistance and recovery ability Methods for characterizing the microstructure of flocs: 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.

[0056] Methods for characterizing shear resistance and recovery: 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: ; ; in, d 1. d 2. d 3 represents the average size (µm) of the flocs at the end of the three stages.

[0057] Experimental results are as follows Figure 13 As shown.

[0058] 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.

[0059] 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. d 3) 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.

[0060] Compared with PDDAC, PDDAC complexed with BE can form larger flocs at low, medium and high salinity, and the size of the flocs remains large after being broken, and the flocs can quickly grow to a larger size after stopping external interference, which makes it can achieve a higher harvest rate after final settlement (the harvest rate under five kinds of salinity is 90.5±0.8%, 91.5±1.5%, 90.4±1.4%, 85.6±1.4% and 81.3±1.0%, respectively). Overall, with the increase of salinity, the size of the flocs in the initial stable period gradually decreases, indicating that salinity affects the force between flocculants and microalgae cells, and thus affects the formation of large-size flocs; after fast stirring and breaking, the size of the flocs formed by PDDAC alone is 80-100 µm, and the size of the flocs formed by the complex group is between 120-140 µm, and the size of the flocs after breaking of the complex group is significantly higher than that of the single PDDAC flocculation group; in the final stable stage, the size of the flocs formed by the single PDDAC group is between 170-260 µm, and the size of the flocs formed by PDDAC complexed with BE is relatively small at 40‰ salinity, but the size of the flocs is between 310-490 µm at 5‰-30‰ salinity, showing excellent re-flocculation ability, which enables PDDAC complexed with BE to maintain excellent flocculation performance at higher salinity environment and achieve ideal settlement effect.

[0061] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. The application of cationic polymer compounded with bentonite for flocculation and harvesting of microalgae with wide salinity, characterized in that, The cationic polymer is polydiallylammonium chloride, and the bentonite is sodium bentonite.

2. The application according to claim 1, characterized in that, When harvesting microalgae through flocculation, the dosage of polydimethyl diallyl 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.

3. A method for harvesting microalgae with a wide salinity range by flocculation of cationic polymers and bentonite, characterized in that, 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.

4. The method for harvesting wide-salinity microalgae by flocculation of cationic polymer compounded with bentonite according to claim 3, characterized in that, 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.

5. The method for harvesting wide-salinity microalgae by flocculation of cationic polymer compounded with bentonite according to claim 3, characterized in that, The amount of polydimethyl diallyl ammonium 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.

6. The method for harvesting wide-salinity microalgae by flocculation of cationic polymer compounded with bentonite according to claim 3, characterized in that, First add polydiallyl ammonium chloride solution, then add sodium bentonite suspension.

7. The method for harvesting wide-salinity microalgae by flocculation of cationic polymer compounded with bentonite according to claim 6, characterized in that, After adding the polydiallyl ammonium chloride solution, stir for 1-5 minutes and then add the sodium bentonite suspension.

8. The method for harvesting wide-salinity microalgae by flocculation of cationic polymer compounded with bentonite according to claim 3, characterized in that, The settling time is 5-15 minutes.

Images