阅读说明：本技术 一种简易的光生物学制氢体系及其制备方法和应用 (Simple photobiological hydrogen production system and preparation method and application thereof ) 是由 柳华杰 陈杰 于 2021-07-22 设计创作，主要内容包括：本发明提供一种简易的光生物学制氢体系及其制备方法和应用,包括以下步骤：向在pH为6～8的微藻液体培养体系中加入絮凝剂,絮凝剂的用量为0.1g/L～100g/L之间,所述微藻液体培养体系为采用液体培养基培养,其中微藻浓度为OD-(750)＝0.3,所述微藻液体培养体系的体积为5ml；絮凝后的微藻液体培养体系中产生微藻细胞聚集体,在光照条件下能够实现光生物学制氢。本发明首次提出使用一种在近中性条件絮凝微藻的絮凝剂制备得到基于微藻细胞聚集体的光生物学制氢体系,解决了光生物学制氢体系制备成本高、流程复杂等问题,有望推动光生物学制氢的实际应用发展。(The invention provides a simple photobiological hydrogen production system and a preparation method and application thereof, and the system comprises the following steps: adding a flocculating agent into a microalgae liquid culture system with the pH of 6-8, wherein the dosage of the flocculating agent is 0.1-100 g/L, and the microalgae liquid culture system adopts a liquid culture medium for culture, wherein the concentration of microalgae is OD 750 The volume of the microalgae liquid culture system is 5 ml; the flocculated microalgae liquid culture system generates microalgae cell aggregates, and the photobiological hydrogen production can be realized under the illumination condition. The invention firstly provides a microalgae cell aggregate-based photobiological hydrogen production system prepared by using a flocculating agent for flocculating microalgae under a near-neutral condition, solves the problems of high preparation cost, complex flow and the like of the photobiological hydrogen production system, and is expected to promote the practical application development of the photobiological hydrogen production.)

1. A simple preparation method of a photobiological hydrogen production system is characterized by comprising the following steps:

s1: adding a flocculating agent into a microalgae liquid culture system with the pH of 6-8, wherein the dosage of the flocculating agent is 0.1-100 g/L, and the microalgae liquid culture system adopts a liquid culture medium for culture, wherein the concentration of microalgae is OD₇₅₀The volume of the microalgae liquid culture system is 5 ml;

s2: the flocculated microalgae liquid culture system generates microalgae cell aggregates, and the photobiological hydrogen production can be realized under the illumination condition.

2. The method for preparing the simple photobiological hydrogen production system according to claim 1, wherein the flocculating agent is any one or a combination of at least two of cationic etherified starch, chitosan and cationic polyacrylamide.

3. The method as claimed in claim 1, wherein the microalgae is green algae selected from Chlamydomonas reinhardtii, Chlorella vulgaris, and Chlorella pyrenoidosa.

4. The method of claim 1, wherein the microalgae in the microalgae liquid culture system in the step S1 is cultured in a liquid culture medium selected from the group consisting of TAP medium, SE medium, and BG11 medium.

5. The method as claimed in claim 1, wherein the microalgae aggregates in step S2 are directly generated in the original microalgae liquid culture system without separation, enrichment or other additional processing steps.

6. The method of claim 1, wherein the size of the microalgae aggregate obtained in step S2 is 50-1000 μm.

7. The method for preparing a simple photobiological hydrogen production system according to claim 1, wherein the illumination condition in step S2 is 1000-10000 Lux illumination.

8. A photobiological hydrogen production system produced by the production method according to any one of claims 1 to 7.

9. Use of the photobiological hydrogen production system according to claim 8 in the development of new energy sources.

Technical Field

The invention relates to the field of photobiological hydrogen production, in particular to a simple photobiological hydrogen production system and a preparation method and application thereof.

Background

The use of traditional fossil fuels causes a large amount of greenhouse gas emissions, and the resulting global climate change is increasingly detrimental to the sustainable development of the life system. For this reason, achieving carbon neutralization has become a common important development goal in countries throughout the world. Hydrogen is used as a fuel, which has high calorific value and brings about only water as a byproduct, and water can be used as a raw material for producing hydrogen, so that hydrogen is regarded as a very promising alternative to fossil fuels. However, hydrogen currently used commercially in the market is still produced from traditional fossil energy sources such as natural gas, and it is still difficult to achieve net zero carbon emissions with the production of large amounts of carbon dioxide.

The photobiological hydrogen production uses the light energy which is abundant in storage on the earth as an energy source, uses water as a production raw material, and uses a renewable organism as a catalyst to realize the preparation of hydrogen, and is a hydrogen preparation method with net zero carbon emission in the whole process, so the photobiological hydrogen production method is more and more concerned. However, the biocatalyst in the photobiological hydrogen production needs an anaerobic environment to have catalytic hydrogen generation activity, but the photosynthesis pathway that the photobiological hydrogen production depends on inevitably generates oxygen, so how to construct an effective anaerobic environment under the illumination condition is the key of the photobiological hydrogen production. The current anaerobic environment forming method for photobiological hydrogen production mainly comprises the steps of adding an oxygen removal substance, depriving sulfur elements and forming microalgae cell aggregates. The cost of adding oxygen-removing substances is high, and sulfur element deprivation needs to realize replacement of a sulfur-free culture medium by centrifugation, so that large-scale preparation at low cost is difficult. The principle of the photobiology hydrogen production system based on the microalgae aggregate is that microalgae cells in the aggregate lack illumination, so that photosynthesis is inhibited and oxygen is stopped to be released, and further, the original oxygen is consumed through the respiration of the cells to form a local anaerobic environment capable of producing hydrogen. Therefore, the microalgae aggregate can realize the photobiological hydrogen production without adding any oxygen removal substance under the condition of a common sulfur-containing culture medium, and is a scheme system with low cost and large-scale application potential. However, in the current stage of preparation of the microalgae aggregates, the surfaces of the microalgae cells need to be chemically modified, the microalgae cells need to be harvested by centrifugal separation in advance, and the large-volume centrifugal process usually wastes time and labor, so that the large-scale application of the microalgae aggregates is limited. The development of a simple microalgae aggregate-based photobiological hydrogen production system is the key to realizing the commercial application of the system.

The principle of microalgae flocculation is to reduce or eliminate electrostatic repulsion on the surface of microalgae by adding a flocculating agent and to make microalgae cells approach each other by adsorption and bridging to form floc settlement. The flocculant is used for constructing the microalgae aggregate-based photobiological hydrogen production system, so that low-cost large-scale application and development of the microalgae aggregate-based photobiological hydrogen production system are expected to be promoted.

Disclosure of Invention

The invention aims to provide a simple photobiological hydrogen production system, a preparation method and application thereof, so as to solve the problems of high preparation cost and complicated operation process of the photobiological hydrogen production system in the prior art.

The invention provides the following technical scheme: a simple preparation method of a photobiological hydrogen production system comprises the following steps:

s1: adding a flocculating agent into a microalgae liquid culture system with the pH of 6-8, wherein the dosage of the flocculating agent is 0.1-100 g/L, and the microalgae liquid culture system adopts a liquid culture medium for culture, wherein the concentration of microalgae is OD₇₅₀The volume of the microalgae liquid culture system is 5 ml;

s2: the flocculated microalgae liquid culture system generates microalgae cell aggregates, and the photobiological hydrogen production can be realized under the illumination condition. The content of oxygen and hydrogen in the photobiological hydrogen production system is monitored by a gas chromatograph.

In the step S1, the dosage of the flocculating agent is limited to be 0.1 g/L-100 g/L. In fact, the amount of the flocculant can be adjusted according to the specific concentration of the microalgae cells, as long as the system can be ensured to produce obvious microalgae cell aggregates. It should be understood that the microalgae cell aggregate is a three-dimensional multi-cell structure formed by the mutual adhesion and agglomeration of microalgae cells, and when the microalgae cells form the aggregate, the microalgae cells in the aggregate consume oxygen through self-respiration, so that an anaerobic environment required by the photobiological hydrogen production is formed.

Preferably, the use amount of the flocculant is preferably 1 g/L-50 g/L, and the flocculation pH condition is preferably 7-7.5.

Further, the flocculating agent is any one or the combination of at least two of cationic etherified starch, chitosan and cationic polyacrylamide. It is to be understood that other flocculants that are capable of flocculating microalgae in near neutral conditions may also be used in the present invention.

Further, the microalgae is green algae, including any one of chlamydomonas reinhardtii, chlorella vulgaris or chlorella pyrenoidosa or a combination of at least two of the chlamydomonas reinhardtii, the chlorella vulgaris or the chlorella pyrenoidosa. It is to be understood that other microorganisms that can produce hydrogen in an anaerobic environment and that can flocculate are equally suitable for use in the present invention.

Further, the microalgae in the microalgae liquid culture system in the step S1 is cultured in a liquid culture medium, wherein the liquid culture medium is any one of a TAP culture medium, an SE culture medium or a BG11 culture medium. Generally, the pH of the culture medium is adjusted to be within the range of 6-8 and is always maintained at 6-8, so that the microalgae is ensured to have catalytic activity for hydrogen production. Because microalgae catalytic hydrogen production requires an anaerobic environment first and then a suitable pH to maintain the catalytic activity of hydrogen production.

Further, the microalgae aggregates in the step S2 are directly generated in the original microalgae liquid culture system without separation, enrichment and other additional processing steps. For example, photobiological hydrogen production can be achieved without the need to collect microalgae aggregates by centrifugation. Because the flocculant provided by the step S1 of the invention can efficiently flocculate the microalgae cells in the liquid culture system to directly generate obvious microalgae aggregates, a local anaerobic environment capable of producing hydrogen can be simply and effectively formed, which has obvious advantages for a large-scale hydrogen production system, and not only reduces the operation steps and the production requirements, but also reduces the production cost.

Further, the size of the microalgae aggregate obtained in the step S2 is 50-1000 μm.

Further, the illumination condition in the step S2 is 1000-10000 Lux illumination.

The invention also provides a photobiological hydrogen production system prepared by the preparation method.

The invention also provides application of the photobiological hydrogen production system in new energy development.

The invention has the beneficial effects that:

1. the method provided by the invention firstly proposes the use of the flocculant for flocculating the microalgae under the near-neutral condition, and directly generates the microalgae cell aggregate in the microalgae liquid culture system, thereby realizing the construction of an extremely simple photobiological hydrogen production system. The experimental result of the invention proves that the photobiological hydrogen production system can continuously produce hydrogen for more than 4 days under the overall aerobic condition. The problems of high preparation cost and complicated operation process of a common photobiology hydrogen production system are well solved.

2. The simple photobiological hydrogen production system solves the problems of high preparation cost and complicated operation process of the common photobiological hydrogen production system. In the prepared photobiological hydrogen production system, microalgae are flocculated in a near-neutral pH environment (pH 6-8) to form microalgae aggregates, and as a result, 4-day continuous photobiological hydrogen production is realized. The invention is expected to promote the low-cost large-scale practical application development of the photobiological hydrogen production.

Drawings

The invention will be described in more detail hereinafter on the basis of embodiments and with reference to the accompanying drawings. Wherein:

FIG. 1 is a schematic diagram illustrating the principle of the present invention that a flocculant induces free dispersed microalgae cells to form microalgae aggregates to produce photobiological hydrogen;

FIG. 2 is a graph showing the results of optical microscope observation of cationic etherified starch in Experimental example 1 of the present invention;

FIG. 3 is a graph showing the result of optical microscope observation of Chlorella pyrenoidosa in Experimental example 1 of the present invention;

FIG. 4 is a Zeta potential diagram of Chlorella pyrenoidosa, a cationic etherified starch and a mixture thereof in Experimental example 2 of the present invention;

FIG. 5 is a statistical chart of the flocculation efficiency results of the cationic etherified starch on Chlorella pyrenoidosa in Experimental example 3 of the present invention;

FIG. 6 is a graph showing the result of observation by an optical microscope of a Chlorella pyrenoidosa aggregate obtained by the production method according to example 1 of the present invention in Experimental example 4;

FIG. 7 is a graph showing statistics on the size distribution of Chlorella pyrenoidosa aggregates obtained by the preparation method according to example 1 of the present invention in Experimental example 4;

FIG. 8 is a statistical graph showing the cumulative hydrogen production yield over time in the resulting photobiological hydrogen production system according to example 1 of the present invention in Experimental example 5;

FIG. 9 is a statistical graph showing the change in oxygen concentration with time in the photobiological hydrogen production system according to the production method of example 1 of the present invention in Experimental example 5;

FIG. 10 is a statistical chart of analysis results of chlorophyll content of Chlorella pyrenoidosa in the photobiological hydrogen production system obtained by the preparation method of example 1 of the present invention in Experimental example 6;

FIG. 11 is a statistical graph showing the results of pH measurement in the photobiological hydrogen production system according to the production method of example 1 of the present invention in Experimental example 7;

FIG. 12 is a statistical chart showing the cell activity analysis results of Chlorella pyrenoidosa flocculated by adding cationic etherified starch to the photobiological hydrogen production system obtained by the preparation method of example 1 of the present invention in Experimental example 7.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

This example provides a simple and readily available method for preparing a photobiological hydrogen production system, it being understood that the flocculants, microalgae, and liquid media selected in this example are, by way of example only and not limitation, cationic etherified starch, chlorella pyrenoidosa, and TAP medium, respectively, first using TAP medium to culture chlorella pyrenoidosa to log phase growth phase, and then to grow the egg to log phase growth phaseAdding cationic etherified starch into a chlorella pyrenoidosa liquid culture system, flocculating the chlorella pyrenoidosa liquid culture system under the condition of near-neutral pH (pH is 6-8) to generate a microalgae liquid culture system with chlorella pyrenoidosa aggregates, wherein the concentration of microalgae is OD₇₅₀The following examples specifically illustrate the effects of the present invention, when the volume of the microalgae liquid culture system is 5ml and then the contents of oxygen and hydrogen in the culture system are monitored by using a gas chromatograph under light conditions. And monitoring the change of the oxygen and hydrogen contents in the photobiological hydrogen production system by using a gas chromatograph. It should be understood, however, that the photobiological hydrogen production system provided according to the present invention is also applicable to larger scales well in excess of 10mL, as long as the feedstock is sufficient, and the scale is not limited.

The gas chromatograph is an Agilent 8860 type gas chromatograph (Agilent technologies in America), a TCD detector is arranged to simultaneously analyze the content of oxygen and hydrogen, the carrier gas is high-purity nitrogen, and the flow rate is 3-30 mL/min.

Wherein the cationic etherified starch (degree of substitution: 0.025-0.03, viscosity: 460-1200, and stain ≤ 0.5) is obtained from Kule bioengineering, Inc., Anhui; cell activity assay kit (HR0489) and chlorophyll content assay kit (GL3175) were purchased from beijing baiolai bock technologies ltd; chlorella pyrenoidosa (GY-D12) and TAP medium were purchased from Shanghai plain Biotech, Inc.

The working principle of the invention is that based on the advantage of the microalgae cell aggregate photobiology hydrogen production, a flocculating agent is added to enable a microalgae liquid suspension culture system to flocculate under the condition of near neutral pH and generate obvious microalgae cell aggregates. Because the surfaces of the microalgae cells are negatively charged, the microalgae cells are difficult to approach each other under the liquid culture condition and are dispersed in the culture system because the charges of the same species repel each other. The flocculant is usually provided with positive charges, and can reduce or eliminate electrostatic repulsion on the surface of microalgae, so that microalgae cells can approach to form an aggregate, and in addition, the cationic etherified starch or cationic polyacrylamide and other polymeric flocculants also have an adsorption and bridging effect, so that the microalgae cell approaching to each other can be promoted, and the microalgae cell aggregate can be formed more effectively. Wherein the purpose of forming the microalgae aggregate is to generate an anaerobic environment in the microalgae aggregate so as to activate the catalytic activity of the microalgae for producing hydrogen. Microalgae hydrogen production depends on intracellular catalase or nitrogenase, and both the catalase and the nitrogenase need an anaerobic environment to have catalytic activity. The free dispersed microalgae cells undergo normal photosynthesis to release a large amount of oxygen, and thus the catalase or nitrogenase is in an inactivated state. After the dispersed microalgae cells form the aggregate, the microalgae cells in the aggregate lack illumination and photosynthesis is inhibited, so that oxygen cannot be released, and the respiration of the cells can still be normally carried out without being influenced by illumination, so that the cells in the aggregate can consume original oxygen through respiration to form an anaerobic environment, so that the activity of catalase or nitrogenase can be activated, and further the construction of a photobiological hydrogen production system based on the microalgae aggregate is realized, as shown in fig. 1; since the hydrogen production activity of the catalase and the nitrogenase needs near neutral pH conditions besides anaerobic environment, a flocculant which flocculates under the near neutral conditions needs to be selected, otherwise microalgae cell aggregates are formed, and hydrogen cannot be produced effectively. After the aggregate-based photobiological hydrogen production system is established, a gas chromatograph is used for monitoring the content of oxygen and hydrogen in the photobiological hydrogen production system.

Experimental example 1

The shape and size of the cationic etherified starch and the chlorella pyrenoidosa were analyzed by optical microscope observation for the photobiological hydrogen production system prepared in example 1; the optical microscopic observation result of the cationic etherified starch is shown in FIG. 2 (scale bar is 30 μm in the figure), the cationic etherified starch is uniformly dispersed in the TAP medium and has a diameter of about 18 μm, the optical microscopic observation result of the chlorella pyrenoidosa is shown in FIG. 3 (scale bar is 30 μm in the figure), the chlorella pyrenoidosa is uniformly dispersed in the TAP medium and has a diameter of about 5 μm;

experimental example 2

For the photobiological hydrogen production system prepared in example 1, Zeta potentials of chlorella pyrenoidosa, cationic etherified starch and chlorella pyrenoidosa mixed cationic etherified starch were analyzed by a Zeta potential tester;

as shown in FIG. 4, the Zeta potential of the Chlorella pyrenoidosa is about negative 20 mV, the Zeta potential of the cationic etherified starch is about positive 25 mV, and the Zeta potential of the cationic etherified starch and the cationic etherified starch is about positive 5 mV, which indicates that the cationic etherified starch can effectively reduce or even eliminate the negative charge on the surface of the Chlorella pyrenoidosa.

Experimental example 3

The flocculation efficiency of cationic etherified starch on chlorella pyrenoidosa was analyzed for the photobiological hydrogen production system prepared in example 1, 5mL of chlorella pyrenoidosa grown in logarithmic phase (OD750 ═ 0.3) was placed in a transparent glass test tube having a volume of 8.5mL, 50mg of cationic etherified starch was added, the tube was sealed and cultured at 25 ℃ under 6300lux illumination, the light absorption value at 750nm of the culture supernatant was analyzed using a microplate reader at the time points (2 hours, 4 hours, 6 hours, 12 hours, 24 hours), and then the flocculation efficiency of cationic etherified starch on chlorella pyrenoidosa was calculated according to the following formula:

flocculation efficiency (%) (ODo-ODn)/ODo × 100;

wherein ODo is the light absorption value at 750nm of protein nucleus chlorella culture solution before adding cationic etherified starch;

ODn is the light absorption at 750nm of the culture supernatant at hour n. As a result, as shown in FIG. 5, the flocculation efficiency of Chlorella pyrenoidosa was more than 80% 4 hours after the addition of the cationic etherified starch, and thereafter, the culture system of Chlorella pyrenoidosa was always maintained in a high flocculation efficiency state.

Experimental example 4

For the photobiological hydrogen production system prepared in example 1, cell aggregates generated by cationic etherified starch flocculation chlorella pyrenoidosa are observed and analyzed by an optical microscope, and the size distribution of the aggregates is statistically analyzed;

as a result, as shown in FIG. 6 (scale 100 μm in the figure), after flocculating Chlorella pyrenoidosa with the cationic etherified starch, remarkable aggregates of Chlorella pyrenoidosa were produced in the original culture system, and as shown in FIG. 7, the aggregate size was intensively distributed around 300 μm, and the maximum size diameter exceeded 800 μm.

Experimental example 5

Placing 5mL of chlorella pyrenoidosa growing in logarithmic phase (OD750 ═ 0.3) into a transparent glass test tube with the volume of 8.5mL, then adding 50mg of cationic etherified starch, sealing the test tube, culturing under the conditions of 25 ℃ and 6300lux illumination, extracting 100 mu L of test tube headspace gas by using an airtight needle at a fixed time point (24 hours, 48 hours, 72 hours and 96 hours), injecting the test tube headspace gas into a sample inlet of a gas chromatograph, analyzing the content of hydrogen and oxygen in a culture system, and detecting the conditions: the TCD detector is 200 ℃, the column incubator is 100 ℃, and the flow rate of the carrier gas is 3 mL/min.

As shown in FIG. 8, the duration of the photobiological hydrogen production system obtained by the preparation method of the present invention was as long as 96 hours (4 days), and it was found from FIG. 9 (in which the circular curve represents the oxygen concentration of headspace gas in the experimental group, the square curve represents the oxygen concentration of free dispersed Chlorella pyrenoidosa culture system, and the oxygen concentration of headspace gas in the control group, after flocculation with cationic etherified starch, that the oxygen content in the culture system capable of producing hydrogen continuously decreased, indicating that the oxygen concentration in the system decreased after flocculation with Chlorella pyrenoidosa to produce aggregates.

Experimental example 6

The culture of Chlorella pyrenoidosa reacted for 96 hours in Experimental example 5 was analyzed for chlorophyll content, after shaking the culture sufficiently, an equal volume (5mL) of a chlorophyll content analysis solution was added, incubated at room temperature for 4 hours with shaking in the dark, and then centrifuged at 1 ten thousand rpm for 15 minutes using a centrifuge, and the filtrate, i.e., a crude chlorophyll substance, was taken out, and the light absorption values of the sample at 665nm (A665) and 649nm (A649) were measured using a microplate reader. According to the following formula:

total chlorophyll content (mg) ═ CT × N × V;

CT＝6.63×A665+18.08×A649；

n is dilution multiple;

v ═ sample system (L);

obtaining the result of the total chlorophyll content of the chlorella pyrenoidosa;

the results are shown in fig. 10, in which the chlorophyll content of the chlorella pyrenoidosa on the left side, namely the chlorophyll content of the chlorella pyrenoidosa after flocculation by adding cationic etherified starch, the chlorophyll content of the experimental group is lower than that of the control group, and the chlorophyll content of the chlorella pyrenoidosa after flocculation by adding cationic etherified starch is lower than that of the chlorella pyrenoidosa on the right side, which indicates that the biosynthesis of chlorophyll is inhibited to some extent after the chlorella pyrenoidosa forms aggregates, and this also laterally proves that the illumination of algae cells in the aggregates is obviously deficient after the chlorella pyrenoidosa forms aggregates, thereby affecting the biosynthesis of chlorophyll;

experimental example 7

Taking 5mL of log-phase-grown (OD750 ═ 0.3) Chlorella pyrenoidosa, placing the strain in a transparent glass test tube with a volume of 8.5mL, adding 50mg of cationic etherified starch, culturing at 25 ℃ under 6300lux illumination, shaking the culture at a fixed time point, then testing the pH of the culture using a pH meter, and taking 200. mu.L of the culture shaken above, adding 20. mu.L of a cell activity assay reagent solution, then incubating for 4 hours at room temperature in the absence of light with shaking, then centrifuging for 15 minutes at a rotation speed of 1 ten thousand revolutions using a centrifuge, taking the filtrate, measuring the light absorption value of the sample at 490nm (OD490) using a microplate reader, and then calculating the following formula:

cell activity (%) - (OD490e-OD490b)/(OD490c-OD490b) × 100;

OD490e is an experimental group, that is, the light absorption of 490nm of the sample after the cell activity analysis reagent solution treatment of the chlorella pyrenoidosa flocculated by adding cationic etherified starch;

OD490c is control group, i.e. light absorption at 490nm of sample of natural free dispersed Chlorella pyrenoidosa treated with cell activity analysis reagent solution;

OD490b is the light absorption at 490nm of the sample after the blank TAP culture fluid is treated with the cell activity assay reagent fluid;

obtaining the cell activity of the chlorella pyrenoidosa in the culture system;

as a result, as shown in FIG. 11, the pH of the chlorella pyrenoidosa culture system flocculated by adding the cationic etherified starch was lower than that of the naturally free-dispersed chlorella pyrenoidosa culture system, but was maintained in a nearly neutral pH range as a whole; as for the cell activity, as shown in FIG. 12, the addition of the cationic etherified starch also reduced the cell activity of the Chlorella pyrenoidosa to some extent, but the effect was not significant, and the cell activity of the Chlorella pyrenoidosa flocculated by the addition of the cationic etherified starch remained relatively maintained at 65% or more after 96 hours.

The above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Furthermore, those skilled in the art will appreciate that while some embodiments herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.