Composite material and method for accelerating diatom sedimentation

Abstract

The invention relates to the field of microalgae sedimentation, in particular to a composite material for accelerating diatom sedimentation and a method thereof. The composite material comprises chitosan and clay, wherein the mass ratio of the chitosan to the clay is (1: 5)-(1: 15). The sedimentation method comprises the following steps: adding the composite material into diatom liquid, culturing for a certain time, and collecting the diatom. By implementing the scheme, the recovery rate of the diatom is improved.

Description

Technical Field

[0001] This invention relates to the field of microalgae sedimentation, and more specifically to a composite material and method for accelerating diatom sedimentation. Background Technology

[0002] Diatoms are key contributors to Earth's primary productivity. As single-celled photosynthetic microorganisms, they are distributed across various types of water bodies globally, from freshwater lakes to high-salinity oceans, and even thrive in extreme environments such as polar ice caps and areas with extremely low silicate concentrations. Thanks to their highly efficient photosynthetic systems and extremely rapid cell renewal rates, diatoms can achieve an annual biomass yield per unit area that is 10-20 times that of terrestrial higher plants. Each kilogram of dried diatoms can achieve a net carbon fixation efficiency of 1.8-2.2 kg CO2, significantly higher than the average level of forest ecosystems. It is estimated that diatoms contribute approximately 20% of global primary productivity and about 40% of marine carbon deposition, making them a crucial "biological pump" for maintaining the global carbon cycle.

[0003] Diatoms have a simple nutrient requirement structure and can grow rapidly in wastewater with low nitrogen, low phosphorus, and even containing heavy metals and rare earth elements. Producing 1 ton of dried diatoms can remove 50-70 kg of nitrogen and 6-10 kg of phosphorus, while reducing chemical oxygen demand (COD) by more than 60%, achieving a synergistic process of wastewater purification and carbon fixation. Their cell walls are composed of nanoscale porous silica (diatom shells), possessing excellent mechanical strength, thermal stability, and a controllable pore size structure, providing a natural template for subsequent material utilization.

[0004] Currently, there are various methods for the pretreatment and enrichment separation of microalgae harvesting, including pre-oxidation, chemical flocculation, sedimentation, filtration, centrifugation, bubble loading, and air flotation, each with its own advantages and disadvantages. Pre-oxidation can induce cells to secrete extracellular polymers, aiding flocculation and sedimentation; however, excessive use of chemicals can cause cell rupture or even death. While chemical flocculation significantly improves separation efficiency, it carries the risk of secondary pollution. Traditional sedimentation, filtration, and centrifugation technologies are limited by low algal concentration and small particle size, generally facing problems such as low efficiency, high energy consumption, high cost, and complex processes, making them difficult to scale up. Air flotation, while simple to operate, does not achieve complete flocculation.

[0005] Currently, flocculation and sedimentation are widely used due to their low cost and simple operation. For example, patent CN202410250370 discloses a settling agent and its composition for harvesting Dunaliella salina. By combining the settling agent with worm cells or worm extract, and co-culturing the settling agent with a suitable density of microalgal cells, the microalgae settle naturally, causing Dunaliella salina to settle rapidly, with a harvest rate of 66.9%. However, worm cells have a narrow environmental tolerance window, high environmental requirements, and non-selective predation, readily feeding on algae, leading to a decrease in algal cell sedimentation rate.

[0006] In summary, there is an urgent need to find a collection method that is environmentally friendly, has a high settling rate, and is low in cost. Summary of the Invention

[0007] The present invention aims to provide a composite material and method for accelerating diatom sedimentation, so as to improve the diatom sedimentation rate.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a composite material for accelerating diatom sedimentation, comprising chitosan and clay, wherein the mass ratio of chitosan to clay is 1:5 to 1:15. Preferably, as an improvement, the clay is one of diatomaceous earth, kaolin, and montmorillonite.

[0009] Preferably, as an improvement, the mass ratio of chitosan to clay is 1:5 to 1:15. Within this range, a high diatomaceous earth settling rate can be ensured while reducing costs. If the ratio is higher than 1:5, the overall viscosity increases, and the chitosan cannot uniformly coat the clay, resulting in poor settling. If the ratio is lower than 1:15, the chitosan coating rate and settling efficiency decrease, and the process and cost are high, failing to fully utilize the synergistic function of chitosan and clay.

[0010] A method to accelerate diatom sedimentation involves adding a composite material to a diatom solution and culturing for 1-3 hours.

[0011] Preferably, as an improvement, the concentration of the composite material in the diatomaceous earth solution is 0.05-0.2 g / ml. If it is below 0.05 g / ml, the sedimentation effect is poor, the sedimentation rate decreases, and the sedimentation time is prolonged. If it is above 0.2 g / ml, the viscosity of the diatomaceous earth solution increases, and turbidity occurs again, affecting the observation and measurement results.

[0012] Preferably, as an improvement, the diatom is *Phaeodactylum tricornutum*.

[0013] Preferably, as an improvement, the algal species density in the diatomaceous earth solution is 5 × 10⁻⁶. 7 —15×10 7 cell / mL.

[0014] Preferably, as an improvement, the algal species density in the diatomaceous earth solution is 7 × 10⁻⁶. 7 —12×10 7 cell / mL.

[0015] Preferably, as an improvement, the algal species density in the diatomaceous earth solution is 9 × 10⁻⁶. 7 —10×10 7 cell / mL.

[0016] Preferably, as an improvement, the method for culturing diatomaceous earth is to add diatoms to the culture medium, shake well, and culture in a light incubator until the algal density reaches the target value.

[0017] The advantages of this solution are as follows: 1. High settlement rate: The settlement rate of this solution can reach up to 99.98%, which is more than 30% higher than the traditional method.

[0018] 2. Low cost: Clay is used as one of the materials, and clay reserves are extremely large, making the cost very low for this amount of sedimentation.

[0019] 3. Environmentally friendly: Chitosan, as a common flocculant, is a natural settling agent for diatoms and will not introduce chemical impurities or toxic substances. Attached Figure Description

[0020] Figure 1 Images of composite materials prepared from different clays and chitosan (from left to right: diatomaceous earth-chitosan, kaolin-chitosan, and montmorillonite-chitosan).

[0021] Figure 2 The final sedimentation effect of *Phaeodactylum tricornutum* in different composite materials. Detailed Implementation

[0022] The following detailed description illustrates the specific implementation method: Example 1 A method for accelerating diatom sedimentation includes the following steps: Material preparation: Chitosan and diatomaceous earth were mixed to obtain a composite material with a mass ratio of chitosan to diatomaceous earth of 1:10.

[0023] Preparation of diatomaceous earth solution: Add *Phaeodactylum tricornutum* to the culture medium, shake well, and incubate in a light incubator until the algal density reaches 9.85 × 10⁻⁶. 7 cell / mL.

[0024] Co-culturing: Add 5 ml of diatomaceous earth solution to a 10 mL culture dish, then add the composite material (0.1 g / mL; 0.5 g) and co-culturing for 2 h, wherein the concentration of the composite material in the diatomaceous earth solution is 0.1 g / mL.

[0025] The settlement rate is 99.98%.

[0026] The "sedimentation rate" involved in this invention is estimated by measuring the cell density and volume of the cells settling at the bottom, estimating the number of cells settling, and using this method to estimate the total number of cells. The ratio of the number of cells settling to the total number of cells is used as the sedimentation rate.

[0027] Example 2 A method for accelerating diatom sedimentation includes the following steps: Material preparation: Chitosan and kaolin were mixed to obtain a composite material, wherein the mass ratio of chitosan to kaolin was 1:8.

[0028] Preparation of diatom solution: Add *Phaeodactylum tricornutum* to the culture medium, shake well, and culture in a light incubator until the algal density reaches 7 × 10⁻⁶. 7 cell / mL.

[0029] Co-culturing: Add 5 ml of diatomaceous earth solution to a 10 mL culture dish, then add the composite material (0.1 g / mL; 0.5 g) and co-culturing for 2 h, wherein the concentration of the composite material in the diatomaceous earth solution is 0.08 g / mL.

[0030] The settlement rate is 99.0%.

[0031] Example 3 A method for accelerating diatom sedimentation includes the following steps: Material preparation: Chitosan and montmorillonite were mixed to obtain a composite material with a mass ratio of chitosan to montmorillonite of 1:12.

[0032] Preparation of diatom solution: Add *Phaeodactylum tricornutum* to the culture medium, shake well, and incubate in a light incubator until the algal density reaches 12 × 10⁻⁶. 7 cell / mL.

[0033] Co-culturing: Add 5 ml of diatomaceous earth solution to a 10 mL culture dish, then add the composite material (0.1 g / mL; 0.5 g) and co-culturing for 2 h, wherein the concentration of the composite material in the diatomaceous earth solution is 0.15 g / mL.

[0034] The settlement rate is 98.3%.

[0035] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A composite material for accelerating diatom sedimentation, characterized in that: Including chitosan and clay.

2. The composite material for accelerating diatom sedimentation according to claim 1, characterized in that: The clay is one of diatomaceous earth, kaolin, or montmorillonite.

3. The composite material for accelerating diatom sedimentation according to claim 1, characterized in that: The mass ratio of chitosan to clay is 1:5 to 1:

15.

4. A method for accelerating diatom sedimentation, characterized in that: The composite material described in any one of claims 1-3 is added to diatomaceous earth solution for cultivation.

5. The method for accelerating diatom sedimentation according to claim 4, characterized in that: The concentration of the composite material in the diatomaceous earth solution is 0.05-0.2 g / ml.

6. The method for accelerating diatom sedimentation according to claim 5, characterized in that: The diatom is *Phaeodactylum tricornutum*.

7. A method for accelerating diatom sedimentation according to claim 6, characterized in that: The algal density in the diatomaceous liquid is 5 × 10⁻⁶. 7 —15×10 7 cell / mL.

8. The method for accelerating diatom sedimentation according to claim 6, characterized in that: The algal density in the diatomaceous liquid was 7 × 10⁻⁶. 7 —12×10 7 cell / mL.

9. A method for accelerating diatom sedimentation according to claim 6, characterized in that: The algal density in the diatomaceous liquid was 9 × 10⁻⁶. 7 —10×10 7 cell / mL.

10. A method for accelerating diatom sedimentation according to claim 9, characterized in that: The method for culturing diatomaceous earth solution is to add diatoms to the culture medium, shake well, and then culture in a light incubator until the algal density reaches the target value.

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