KR101516797B1 - Method for Flocculating Microalgae - Google Patents

Abstract

The present invention relates to a microalgae flocculation method, and the present invention provides a microalgae flocculation method using an economical and easy-to-operate method. The microalgae of the present invention can be used as useful biomass for the production of biodiesel, and the obtained microalgae are alternative energy sources, providing sustainable resources free from depletion.

Description

{Method for Flocculating Microalgae}

The present invention relates to a microalgae flocculation method.

Most of the energy consumed worldwide is supplied by fossil fuels such as petroleum, coal, and natural gas. However, the amount of crude oil that can be collected is limited, and the carbon dioxide generated during the burning of fossil fuels causes severe environmental problems called climate change as a main cause of global warming. As a result, countries around the world are focusing on developing alternative energy using biomass materials to replace fossil fuels [1-3].

Bio-energy, one of the alternative energy sources, can be divided into biodiesel, bio-ethanol, and biogas. Biodiesel can be produced from biomass using land plants such as corn, canola, oil palm or jatropha. In addition, microalgae, a third-generation energy source, has high lipid content and is used as a biomass for biodiesel production [4]. Microalgae are characterized by high production yield per area and short cultivation time and cultivation time [5-7]. In order for microalgae to convert to biodiesel, it must go through numerous processes. First, microalgae are cultivated in large quantities and only algae are harvested from the culture. Biodiesel is produced by extracting lipids from harvested algae and converting them from biodiesel to biodiesel. Harvesting is an important factor in biodiesel production, and harvesting efficiency and cost are economically important. Inefficient harvesting methods affect waste as well as environmental pollution [8]. Methods for harvesting microalgae include filtration, flocculation, sedimentation, centrifugation, and Dissolved Air Floatation (DAF). All harvesting methods require a lot of energy with current technology. Harvesting efficiency is not always good because of the high energy. In the case of filtration, it is necessary to replace the membrane periodically because fouling of the filter itself occurs over time. In the case of the precipitation method, the energy cost is low, but it takes a long time and the harvesting efficiency is not good. In centrifugation, the amount of energy used is high and it is not suitable because of high maintenance cost [9-10].

Numerous papers and patent documents are referenced and cited throughout this specification. The disclosures of the cited papers and patent documents are incorporated herein by reference in their entirety to better understand the state of the art to which the present invention pertains and the content of the present invention.

The present inventors have sought to develop a method for rapidly and economically aggregating microalgae, especially Tetraselmis sp., A third generation biomass. As a result, it was confirmed that when the chitosan aqueous solution was added to the culture medium containing tetracellmis, it was possible to efficiently flocculate, and by optimizing the conditions, the present invention was completed.

Accordingly, an object of the present invention is to provide a microalgae flocculation method.

Another object of the present invention is to provide microalgae aggregates.

Other objects and advantages of the present invention will become more apparent from the following detailed description of the invention, claims and drawings.

According to one aspect of the present invention, the present invention provides a microalgae flocculation method.

The present inventors have sought to develop a method for rapidly and economically aggregating microalgae, especially Tetraselmis sp., A biomass, a third generation biomass. As a result, it was confirmed that when the chitosan aqueous solution was added to the culture medium containing tetracellmis, it was possible to efficiently flocculate, and by optimizing the conditions, the present invention was completed.

The microalgae flocculation method of the present invention will be described step by step.

Step (a): preparation of microalgae

In the present invention, a culture medium containing microalgae to be agglutinated is prepared.

The microalgae flocculation method of the present invention is directed to various microalgae that can be used as biomass.

According to one embodiment of the invention, the microalgae are tetra cell Miss (Tetraselmis) species, while Chitose Ross (Chaetoceros) species, Chlorella (Chlorella) species, two Canary Ella (Dunaliella) species, iso Cri sheath (Isochrysis) species According to, nanno claw drop system (Nannochloropsis) species, Spirulina (Spirulina) species, skeletal retrograde nematic (Skeletonema) species, creep Te coordination nieom (Crypthecodinium) or Tallahassee Please Shirakawa (Thalassiosira) paper and, another embodiment of the invention, The microalgae are Tetracellis species.

The culture medium that can be used in the present invention may be any culture medium used for microalgae culture in the art.

The culture medium containing the microalgae of the present invention may contain artificial seawater, fresh water, brackish water, highly saline water or marine water in the culture medium.

According to one embodiment of the invention, the culture medium is a carbon source ^{_{(e.g., CO 2, HCO 3 -,}} CO 3 2 -), a nitrogen source (for example, NO ₃ ^-, urea, amino acids, N2), person (e.g., a hydro Calcium, sodium, magnesium), trace elements (e.g., iron, zinc, manganese, lead, cadmium), vitamins (such as, for example, , Vitamin B, vitamin C, vitamin E).

Step (b): generation of microalgae aggregates

Next, an aqueous chitosan solution is added to the culture medium to produce microalgae aggregates.

The aqueous chitosan solution is prepared by dissolving chitosan in a 0.1 M hydrochloric acid solution and diluting the chitosan with distilled water when the chitosan is completely dissolved.

According to one embodiment of the present invention, the aqueous chitosan solution is added at a concentration of 0.4 to 0.6 mg / ml.

According to another embodiment of the present invention, the aqueous chitosan solution has a concentration of 0.40 to 0.59 mg / ml. According to a specific embodiment of the present invention, the chitosan aqueous solution has a concentration of 0.40 to 0.58 mg / According to a particular embodiment, the aqueous chitosan solution has a concentration of 0.40 to 0.57 mg / ml.

When the chitosan aqueous solution is treated at a concentration of less than 0.4 mg / ml, it exhibits a flocculation efficiency of 60% or less and exhibits flocculation efficiency of 80-90% at a concentration of 0.4 to 0.6 mg / ml.

Further comprising the step of adjusting the pH of the culture medium of step (a) from pH 6.5 to pH 8.5 before said step.

According to an embodiment of the present invention, the pH of the culture medium exhibits a flocculation efficiency of 70% or more when the pH is from pH 6.5 to pH 8.5, and a flocculation efficiency of less than 70% when the pH is below 6.5 or exceeds pH 8.5.

According to another embodiment of the present invention, the pH of the culture medium is from pH 6.7 to pH 8.0. According to a specific embodiment of the present invention, the pH of the culture medium is pH 6.7 to pH 7.5, According to the example, the pH of the culture medium is pH 6.7 to pH 7.3.

The pH of the culture medium of the present invention can be adjusted by adding hydrochloric acid or sodium hydroxide.

According to one embodiment of the present invention, the culture medium, hydrochloric acid aqueous solution and aqueous sodium hydroxide solution at the time of adjusting the pH are at room temperature.

(c) Obtaining microalgae agglomerates

Finally, microalgae aggregates produced by the addition of the aqueous chitosan solution are obtained.

The microalgae agglomerates obtained by the microalgae agglomeration method of the present invention have a flocculation efficiency of 70% or more. The microalgae aggregates obtained may be used as biomass.

According to another aspect of the present invention, the present invention provides a microalgae aggregate.

Since the microalgae aggregates of the present invention are microalgae aggregates obtained by the microalgae aggregation method, the description common to both of them is omitted in order to avoid the excessive complexity of the present specification.

The features and advantages of the present invention are summarized as follows:

(a) The present invention provides a method for flocculation of microalgae using an economical and easy-to-operate method.

(b) The microalgae of the present invention can be used as useful biomass for the production of biodiesel.

(c) The microalgae obtained through the microalgae agglomeration method of the present invention are alternative energy sources, providing a sustainable resource free from depletion.

Figure 1 shows the effect of chitosan concentration on the coagulation efficiency of Tetracellis species.
Figures 2a to 2d show the aggregation of tetracellmis when various concentrations of chitosan are added. Figs. 2A to 2D are images of a case where chitosan concentration of 0.2 mg / ml, 0.3 mg / ml, 0.4 mg / ml and 0.5 mg / ml, respectively, was treated.
Figure 3 shows the influence of the pH of the culture medium on the aggregation efficiency of Tetracellis spp.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are only for describing the present invention in more detail and that the scope of the present invention is not limited by these embodiments in accordance with the gist of the present invention .

Example

Materials and Methods

Microalgae and reagents

The species of microalgae used in the experiment were Tetraselmis sp . , Tetraselmis. KCTC 12236BP). Tetracellis species were cultured in Inha University and the experiment was carried out. The composition of the culture solution is shown in Table 1. The components of Table 1 were dissolved in water to prepare a culture solution.

The concentration of the culture solution was used after diluting the absorbance (expressed as OD below the optical density) of the culture solution to 1 or less in consideration of the Beer-Lambert limit.

Both the chitosan used to agglomerate microalgae and the 0.5M NaOH and 0.5M HCl reagents used for pH control were purchased from Sigma-Aldrich Korea (St. Louis, MO, USA). Since chitosan itself does not dissolve in the culture solution, it was separately prepared as an aqueous solution. To prepare the aqueous solution, add 0.1 g of chitosan to 10 ml of 0.1 M HCl, wait for about 1 hour until the chitosan is completely dissolved. 10 ml of completely dissolved chitosan was again diluted in 100 ml of distilled water to prepare an aqueous chitosan solution having a concentration of 0.1 mg / ml.

Jar test and pH control method

The jar test was conducted to determine the amount of coagulant injected for microalgae aggregation. The microalgae Tetracellis species were placed in five 500 ml Erlenmeyer flasks. After the addition of chitosan in different concentrations, the mixture was rapidly stirred at 180 rpm for 5 minutes and then slowly stirred at 80 rpm for 20 minutes. The number of embryos of each Erlenmeyer flask was sampled and the OD was measured and converted into a percentage (%), and then the coagulant injection rate of the Erlenmeyer flask with the best flocculation efficiency was determined as the optimum value. Experiments were conducted to investigate the effect of culture pH on microalgae aggregation. All experiments were carried out at room temperature (25 ° C) and 500 ml microalgae culture was injected into a 500 ml Erlenmeyer flask. The experiments were carried out using 0.5 M HCl from pH 4 to pH 6 and 0.5 M NaOH from pH 8 to pH 10 based on the pH of the culture medium. After the addition of HCl or NaOH, the agitation speed was allowed to stir at 180 rpm for 30 minutes to allow the flocculant to mix well with the culture medium. After stirring was completed, it was precipitated for 30 minutes.

Coagulation Efficiency Measurement Method

The concentration of microalgae was measured by Beer-Lambert's law using a UV / vis spectrophotometer (Shimadzu BioSpec-mini, Japan). Before the agitation, the supernatant was collected from the surface of the microalgae culture solution under 3 ° C and the absorbance was confirmed using a UV / vis spectrophotometer. After the stirring, the supernatant liquid was collected 3 ㎝ from the water surface as before the agitation, and the absorbance was measured using a UV / vis spectrophotometer. The concentration of microalgae was determined using the measured absorbance before and after flocculation. At this time, the wavelength of the microalgae tetrasell species was measured at 640 nm, and the concentration was converted to the concentration according to the linear relationship between the absorbance and the microalgae concentration, and the degree of coagulation was defined as the coagulation efficiency. :

Coagulation efficiency (%) = [OD ₆₄₀ (t ₀ ) OD ₆₄₀ (t) / OD ₆₄₀ (t ₀ )] x 100

The " OD _{640 "} (t) 'is the microalgae concentration of the supernatant below 3 cm from the surface of the water after stirring, and' OD ₆₄₀ (t ₀ ) 'is the microalgae concentration of the supernatant below 3 cm from the water surface before agitation.

pH  How to measure

The pH was measured using a pH meter (Mettler-Toledo InPro3030, Swiss). Prior to the use of the pH meter, calibration was first performed to increase the reliability of the experiment.

Results and Discussion

Self test method

In 5 Erlenmeyer flasks containing microalgae tetracellular medium, chitosan aqueous solutions were added to 5 flasks at concentrations of 0.1, 0.2, 0.3, 0.4, and 0.5 mg / ml, respectively. Experiments were carried out at 180 rpm for 5 minutes and at 80 rpm for slow stirring. After agitation, the sedimentation time was 30 minutes, and the absorbance was measured every 10 minutes to calculate the flocculation efficiency. As can be seen from FIG. 1, the agglomeration efficiency was over 80% from the addition of chitosan over 0.4 ㎎ / ㎖, and the agglutination efficiency was over 90% at the concentration of 0.5 ㎎ / ㎖. Fig. 2 shows agglutination photographs of microalgae.

As a result, the microalgae agglomeration efficiency was over 80% at the concentration of 0.4 ㎎ / ㎖ or higher.

In case of coagulation experiment, it was economical to use chitosan as small as possible. Therefore, the coagulation experiment was carried out in a small amount and the coagulation efficiency exceeded 90% even at a concentration of 0.5 ㎎ / ㎖.

pH Of microalgae

Experiments were carried out to investigate the effect of pH on the aggregation of chitosan added to marine microalga species Tetracellis species. Experiments were carried out after adjusting the pH of the culture medium by adding 0.5 M HCl or 0.5 M NaOH. In order to examine the influence of pH on the cohesion, the experimental conditions were varied only in pH, and the amount of the remaining microalgae culture medium and the amount of temperature coagulant chitosan (0.4 ㎎ / ㎖) were all under the same conditions.

FIG. 3 shows the maximum aggregation efficiency at a pH of 7 in the case of the microalgae tetrasell mist.

As a result, it was concluded that the microalgae Tetracellis species had the best flocculation efficiency at pH 7.

conclusion

The microalgae Tetracellis species showed the maximum flocculation efficiency at pH 7 when the pH was adjusted with 0.5 M HCl and 0.5 M NaOH. The microalgae aggregation using chitosan showed the concentration of chitosan exceeding 0.4 ㎎ / ㎖ It was confirmed that the coagulation efficiency was 80% or more. Also, it was concluded that the effect of pH on coagulation efficiency is very high.

In this study, microalgae were coagulated with chitosan, a natural organic coagulant, and the coagulation efficiency was over 80% at chitosan concentration over 0.4 ㎎ / ㎖. The microalgae agglomeration method without inorganic flocculant can solve the environmental problems caused by the use of flocculant, which is expected to be linked to the more environmentally friendly and industrial biodiesel productivity.

references

1. L. Brennan, and P. Owende (2010) Biofuels from microalgaeA review of technologies for production, processing, and extractions of biofuels and co-products. Renew . Sustain . Energ . Rev. 14: 557-577

2. ABM Sharif Hossain, and A. Salleh (2008) Biodiesel fuel production from algae as renewable energy. Am . J. Biochem . Biotech . 4: 250-254.

3. A. Szklo, and R. Schaeffer (2006) Alternative energy sources or integrated alternative energy systems? Oil as a modern lance of Peleus for the energy transition. energy engineering and research . 31: 2513-2522

4. Y. Chisti (2007) Biodiesel from microalgae. Biotechnol . Adv . 25: 294-306.

5. R. Raja, S. Hemaiswarya, A. Kumar, S. Sridhar, and R. Rengasamy (2008) A perspective on the biotechnological potential of microalgae. Crit . Rev. Microbiol . 34: 7788

6. AK Lee, DM Lewis, and PJ Ashman (2009) Microbial flocculation, a potentially low-cost harvesting technique for marine microalgae for the production of biodiesel. J. Appl . Phycol. 21: 559-567.

7. CG Dismukes, D. Carrieri, N. Bennette, GM Ananyev, and MC Posewitz (2008) Aquatic phototrophs: efficient alternatives to land-based crops for biofuels. Curr . Opin . Biotechnol. 19: 235240.

8. P. Somasundaran, and T. Hubbard (2006) Encyclopedia of 표면 and colloid science . 2nd ed., Pp. 2588-2591. CRC Press, Taylor & Francis Group, NY, USA.

9. N. Uduman, Y. Qi, MK Danquah, GM Forde, and A. Hoadley (2010) Dewatering of microalgal cultures: A major bottleneck to algae-based fuels. J Renew Sustain Energy . 2 (1): 012701012701.

10. R. Kurane, and H. Matsuyama (1994) Production of a bioflocculant by mixed culture. Biosci . Biotechnol . Biochem . 58: 1589-1594.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the present invention. It is therefore intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims (8)

A microalgae flocculation method comprising the steps of:
(a) preparing a culture medium containing microalgae;
(a-1) adjusting the pH of the culture medium to pH 6.7 to pH 7.5;
(b) adding an aqueous chitosan solution having a concentration of 0.4 to 0.6 mg / ml to the culture medium to produce microalgae aggregates; And
(c) obtaining the microalgae aggregate; And,
The microalgae is Tetraselmis sp.
delete delete delete delete The method according to claim 1, wherein the pH of the culture medium is adjusted by adding hydrochloric acid or sodium hydroxide. delete delete

Images