JP2001161347A - Microalga for fixing carbon dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a microalga growable even under conditions of CO2 concentration, NOX concentration and SOX concentration comparable to those of various fossil fuel flue gases in thermal power plants, etc., or strong light in the summer season and high temperatures and to provide a method for culturing the microalga. SOLUTION: This microalga Chlorella sorokiniana HO-1 strain is growable under at least one condition selected from the group consisting of an NOX concentration up to 200 ppm, an SOX concentration up to 50 ppm, a light intensity at 1,000-2,000 μmol.m-2.s-1 and 35-49 deg.C temperature and under conditions of 5-20 vol.% CO2 concentration. The method for culturing the microalga comprises aerating the above microalga in a culture tank (a helical tubular reactor, etc.), with a gas at 5-20 vol.% CO2 concentration (thermal power plant flue gases, etc.).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microalgae for fixing carbon dioxide, and more particularly to a greenhouse that can be used for fixing carbon dioxide in various fossil fuel combustion exhaust gas in a thermal power plant or the like and is derived from human activities. The present invention relates to a microalga that can contribute to reduction of emission of an effect gas and a culture method thereof.

[0002]

2. Description of the Related Art Microalgae is a general term for lower plants that mainly consist of single cells and perform photosynthesis. Although the types of microalgae are diverse and have various potentials, examples used at the industrial level to fix carbon dioxide (CO ₂ ) in fossil fuel exhaust gas from thermal power plants and the like are: rare. In the past, Tokugawa Biological Research Institute has cultivated microalgae with flue gas burning city gas, but fixed CO
_{(2) The} amount was small, and the fuel cost was too high, which did not lead to industrialization. From the viewpoint of microalgae utilization, chlorella and spirulina are currently health foods, while
-It is industrialized for the production of carotene. However, acetic acid and inorganic carbonate are mainly used as a carbon source for these cultures, and CO ₂ in exhaust gas is not used. In consideration of such a situation, the present applicant has isolated a microalga that can be used for fixing CO ₂ in fossil fuel combustion exhaust gas in a thermal power plant or the like, and has filed an earlier application (Japanese Patent Application Laid-Open No. Hei 5-
No. 304945). The publication states that CO ₂ in exhaust gas
The immobilized CO ₂ fixation product feed and industrial SCP (Si
U.S. Pat. However, the microalgae can have relatively high NO _x (nitrogen oxide, knock) or SO _x (sulfur oxide, Under the condition of sock) concentration, it could not grow stably and there was a problem that the application scene was limited. Therefore, there is a strong demand for microalgae that can stably grow even under high-light conditions and high-temperature conditions in summer or under the same SO _X and NO _X concentrations as in exhaust gas from thermal power plants using coal or oil as fuel.

[0003]

In order to industrially fix CO ₂ derived from fossil fuel combustion gas discharged in large quantities from a thermal power plant or the like using the CO ₂ fixing ability of microalgae, An important key is to use microalgae that function efficiently even under conditions where exhaust gas is directly introduced into the culture tank. Here, the microalgae have a CO ₂ concentration equivalent to that in exhaust gas derived from the combustion of various fossil fuels in a thermal power plant,
O _X concentration should also be grown in SO _X concentration conditions. In addition, it is advantageous in terms of cost reduction to cultivate microalgae outdoors using sunlight.However, when cultivating outdoors, if the temperature of the culture solution rises excessively under strong insolation conditions in summer, But maintaining high productivity
This is extremely important in reducing the cooling load. The present invention, CO ₂ concentration is equivalent to various fossil fuels exhaust gases in a thermal power plant or the like, NO _X concentrations and SO _X concentration and, possible growth of micro-algae and incubated at high light and high temperature conditions in summer The task was to provide a method.

[0004]

The present inventors have conducted various studies and found that relatively high concentrations of CO ₂ , NO _X and SO _{2 were obtained} .
_X resistant, even at high light intensity and high temperature
Microcultures that can stably grow are separated and purified, and even in cultures in which gas simulating exhaust gas from thermal power plants is aerated,
The microalgae were found to proliferate sufficiently with almost no decrease in CO ₂ fixation ability, and further studied diligently to complete the present invention.

That is, the present invention relates to
NO_XConcentration, SO up to 50 ppm _XConcentration, 1000-
2000μmol ・ m^-2・ S^-1Light intensity and 35-4
At least one selected from the group consisting of 9 ° C.
Conditions and 5-20% by volume of CO_TwoGrow under concentration conditions
Regarding possible microalgae. NO in the present invention_X, S
O_XAnd CO_TwoEach concentration of the gas to be aerated during culture
It is a numerical value based on the inside dry gas. 200p
NO to pm_X, SO up to 50 ppm_XAnd / or
Or 5-20% by volume of CO_TwoAeration of gas containing
The microalgae of the present invention, which can grow, can be used in thermal power plants, etc.
Fossil fuel combustion exhaust gas directly into the culture tank
It means that it can be cultured. Note that NO_XIs NO, NO
_TwoIs a generic term for nitrogen oxides such as_XIs SO_Two, SO
_Four ^2-, S_TwoIt is a general term for sulfur oxides such as O and SO.
In exhaust gas from power plants _XAnd SO_XMain component of
Are NO and SO respectively_TwoIt is. In addition, the present invention
The light intensity at the top of the culture vessel
Average light intensity. 1000-2000 μmol · m^-2
・ S^-1The microalgae of the present invention, which can grow even at a light intensity of:
Directly illuminating the mid-summer sunlight in summer in Japan
Also means that they can proliferate. 35-49 ° C
At this culture temperature, most conventionally known microalgae grow
Although it is not possible to grow in such a high temperature area,
Ming microalgae can be cultured in culture
Even if the temperature rises, external cooling is required.
Absent. That is, the microalgae of the present invention can reduce the cooling load during culture.
It is possible to reduce. In the present invention, "raw
`` Can grow '' means that it grows under normal atmospheric ventilation conditions.
Growing at or equal to
It means to grow on. Also, the microalgae of the present invention
The pH of the culture solution to be cultured is in a range suitable for the microalgae, usually
It is preferable to keep it at 4 to 7, especially around 6.
Needless to say. In particular, SO_XA place to aerate the contained air
In this case, the culture solution tends to be acidic.
Needs to be adjusted to 4 to 7, especially around 6.

[0006] The present inventor has determined that hot spring water from various sampling sites can be used.
It can grow under high temperature conditions using soil or soil as a separation source
A new strain of Chlorella is purely isolated and has high CO2_Two,
NO _XOr SO_XConcentration or under conditions of high light intensity
The strain was found to be able to grow stably, and the strain was
Homology with Rera 18S ribosomal RNA gene sequence
Comprehensive comparison and morphological observation with transmission electron microscope
From the perspective of Chlorella Solokiniana
sorokiniana). And the above strain is HO
-1 strain. In addition, at present,
The Institute of Industrial Technology does not accept algae,
The above strain HO-1 has not been deposited.

The microalgae of the present invention can grow without a special carbon source such as acetic acid or carbonate other than CO ₂ , and therefore can fix and assimilate CO ₂ . Therefore, the present invention relates to a method for culturing microalgae, which comprises aerating a gas having a CO ₂ concentration of 5 to 20% by volume to the culture solution of microalgae according to the present invention. In this method, the gas to be aerated may be, for example, various exhaust gases generated when fossil fuels are burned, and particularly include thermal power station exhaust gases.
In addition, the microalga of the present invention does not cause any problem even if cultured in a normal culture tank, but because it performs photosynthesis during growth,
In order to enable the photosynthesis to be performed with higher efficiency, a colorless and transparent tube such as a plastic tube or a glass tube is spirally wound as a culture tank (hereinafter referred to as a spiral tubular reactor). Is also preferable. The spiral tubular reactor may be a tube in which a tube is wound in a cylindrical shape, but it is preferable to wind the tube in a conical shape, since light is uniformly applied to the entire reactor.

[0008] Generally, microalgae are proteins, in which about half of the substances constituting the algal bodies are proteins, and can be sufficiently used as industrial proteins or raw materials thereof, or as highly nutritious feeds. Therefore, the protein content contained in the microalgae, which is a carbon dioxide fixation product of the microalgae of the present invention,
It is expected to be about half of the dry weight. Therefore, the possibility that the microalgae of the present invention can be used as a highly nutritious feed or industrial protein (or a raw material thereof) is sufficiently high.

[0009]

DETAILED DESCRIPTION OF THE INVENTION HO, a kind of microalgae of the present invention,
During the flat culture flask -1 strain, the CO ₂ concentration of 10 or 15%
All showed active growth. The optimum temperature at this time was 35 ° C., but good growth was shown even at 40 ° C. Further, growth was possible for a short time up to 45 ° C., and the optimum pH value was about 6.0. 10% CO
100ppmNO and 25ppmSO ₂ to ₂ enriched air
10% even if either or both are mixed and ventilated
Maximum specific growth rates and final algal densities comparable to those with CO ₂ enriched air alone were obtained. Further, in a spiral tubular reactor obtained by winding a HO-1 strain, which is a kind of microalgae of the present invention, into a conical vinyl chloride tube, the standard solar radiation conditions of Japan (about 980 μmol · m ^−2.
By the indoor culture simulating s ^-1 ), productivity of up to 34.2 g dry matter / m ² installation area / day was achieved, and the photosynthetic efficiency was extremely high at 8.64%. Furthermore, indoor culture (maximum temperature of the culture solution 46.5 ° C.) simulating the strongest light conditions in summer (about 1700 μmol · m ⁻² · s ⁻¹ )
It showed good productivity and confirmed growth at 48.7 ° C. 100 ppm NO in 10% CO ₂ enriched air
Also, when one or both of 25 ppm SO ₂ and 25 ppm SO ₂ were mixed and aerated, and the indoor culture was performed simulating the standard solar radiation conditions, the microalga of the present invention maintained high values in both productivity and photosynthetic efficiency. From these facts, the microalgae of the present invention can be applied not only to the exhaust gas of LNG thermal power plants that do not contain SO _X but also to fix CO _{2 in} the exhaust gas of coal and oil thermal power plants that contain SO _X , Further, since it shows extremely high photosynthetic productivity even under high temperature and strong light, it is clear that it has a great advantage in culturing outdoors in summer and reducing the cooling load.

[0010]

The present invention will be described in more detail with reference to the following examples.
However, the present invention is not limited to these examples.
Absent. Example 1 Separation and Classification of Microalgae (Separation of Microalgae) Nature of Microalgae Grown Under High Temperature Conditions
Separation from the world was performed according to the following method. As a separation source
Hot spring water or soil collected from Hakone Town, Kanagawa Prefecture (all
8 types). 1 ml if the sample is liquid, soil
In the case of (1), 1 g by wet weight is added to the MBM liquid medium (Table 1) 15
inoculate a test tube containing 4 ml, and incubate at 40 ° C. for 4 weeks.
Pre-placement culture was performed. Continuous irradiation using white fluorescent light as a light source
The light intensity condition is 30 μmol · m^-2・ S^-1And
Using the sample after completion of the preculture, under the same light conditions, 10% CO2
_Two5 days of enrichment culture at 40 ° C using enriched air
Was done. Microalgae growth confirmed in enrichment culture
Diluted sample with sterile water, and dilute each diluted solution with MBM agar medium.
Ground (1.5% agar added to the above MBM liquid medium)
) And cultured at a temperature of 26 ° C. for 2 weeks. light
Irradiation is performed using a white fluorescent lamp as a light source, every 12 hours in a light / dark cycle.
(12 hours light condition), the light intensity at the time of light is 120 μmol
・ M^-2・ S ^-1The culture was performed as follows. After colony formation, simply
Isolate one colony, subculture on MBM Slope Agar,
This was designated as an isolate. In addition, mixed bacterial strains
I confirmed that there was no entry.As a result of the above operation, out of the eight collected samples, two samples
Algae were isolated, of which isolates grew higher
Was named HO-1 strain and used for the following experiments.
Was. The sample used as the source of the HO-1 strain was isolated from Kanagawa Prefecture.
It is hot spring water of iron spring of Owakudani in Hakone-machi, temperature is 43 degrees Celsius
(Raw water temperature 63 ° C.) and pH 7.28. Optical microscopy
As a result of observing the morphology of the isolate using a mirror,
Was found to be Chlorella. However, optical microscopy
Species level identification was not possible with mirror morphological observation
Next, morphological observation with a transmission electron microscope and 18S r
-Perform RNA gene sequence analysis at the species level of isolates
Was attempted. (Electron microscopy observation) Shape of the isolate by transmission electron microscopy
The state observation was performed according to the following method. Prefix is 0.05
Using 2% glutaraldehyde in M phosphate buffer,
The reaction was performed at pH 7.0 and a temperature of 4 ° C. for 2 hours. Post fixation is 0.0
Using 2% osmium tetroxide in 5M phosphate buffer, p
H7.0 at a temperature of 4 ° C. for 2 hours. Acetone series
After water, embedding was performed using Spurr resin. Ultra-thin section
After preparation, use 4% uranyl acetate for 15
Stained for minutes and washed with water. In addition, use 0.4% lead citrate
For 15 minutes at room temperature. After washing with water,
Photograph of the isolate at an accelerating voltage of 80 kV using a scanning microscope
Was done. The photograph obtained is shown in FIG. Cell shape is sphere
The size was about 3 to 8 μm in diameter. (Determination of base sequence of ribosomal RNA) 18S of isolated strain
The determination of the r-RNA gene sequence was performed according to the following method.
Was. First, to isolate genomic DNA from the isolate,
Isoplant DNA extraction with benzyl chloride
The test was performed using a kit (Nippon Gene). Isolated
ExTaq DNA polymerase using genomic DNA as template
PCR of genomic DNA was carried out using ROS (manufactured by Takara Shuzo). Already
Considering the known 18S r-RNA gene of Chlorella,
The following two types of CR primers were used: F5'-aacctggttgatcctgccagtagtc-3 'R5'-ttgatccttctgcaggttcacctac-3'. PCR amplified fragment confirmed by electrophoresis
Thereafter, the gene fragment was transferred to a pGEM-T vector (Promega).
Ligation. Escherichia coli JM as vector host
109 strains were used. After cloning, 18S r-RN
Plasmid having the A gene sequence was inserted into Plasmid
Prepared with Miniprep kit (Bio-Rad)
Was. Sequence the prepared sample using a sequencer.
Was. As a result, the 18S r-RNA gene
The row is 1797 bp and the GC content is 49.75 mol
%Met. 18S r-RNA inheritance of known chlorella
When a homology search was performed with the child sequence, Chlorella
Homology with Rokiniana (Chlorella sorokiniana)
99.7%, Chlorella vulgar
99.5% homology to is), Chlorella kessleri
(Chlorella kessleri) with 97.9% homology
With Chlorella saccharophila
Was 94.6%. Transmission electron microscope
Morphological observation and 18S r-RNA of known chlorella
As a result of comparison of homology with the gene sequence, the above isolate (HO
-1 strain) belongs to Chlorella solokiniana
I decided to.

Example 2 Culture Characteristics of Microalgae Isolate (Experimental Method) The culture characteristics of the isolated chlorella were measured using a flat culture bottle.
Batch culture for 3 days using_TwoConcentration, culture solution
Of the effects of temperature and initial pH on algal growth
Was. NO and SO_TwoEffect on algal growth by 10%
CO_TwoThe examination was conducted at a temperature of 35 ° C. under the conditions. NO and SO
_TwoWas ventilated only under light conditions. C aerated in culture
O_Two, NO, SO_TwoShould be set from the following viewpoints.
Was. Regarding exhaust gas from fossil fuel combustion plant, NO
_XAnd SO_XOf the country based on the Air Pollution Control Law
Emission standards are set, but in fact, coal, heavy crude oil, L
CO contained in NG thermal power plant exhaust gas_TwoConcentration (dry
9.0-14.4%, NO_XConcentration (coal fire
Power O_Two= 6%, heavy crude oil power O_Two= 4%, LNG thermal O_Two
= 5%) is 6 to 198 ppm (NO in exhaust gas)._XMajor
Component is NO), SO_XSO that is the main component of_TwoDark
The degree (dry gas base) is 8 to 220 ppm and each
It varies greatly from plant to plant. Regarding emission standard values
Furthermore, emission standards agreements have been signed with prefectures and municipalities.
And new power plants are realistically
In many cases, emissions are controlled to less than half of the emission standards.
No. In consideration of the above, in this embodiment, the air is enriched.
CO_Two, NO, SO_TwoOf 10%, 1
00 ppm and 25 ppm were set. Light irradiation is white fluorescent
Using a lamp as a light source, 120 μmol every 12 hours of light / dark cycle
・ M ^-2・ S^-1The culture was performed at a light intensity of 1. Initial alga inoculation concentration
The degree is 0.05g dry weight ・ L ^-1And 100 ml of MB
Using M liquid medium, aeration volume 40 ml min^-1Cultured in
Was. To measure the dry weight of algal cells and the pH of the culture solution,
Sampling was performed every 12 hours and analyzed. Algal
The dry weight is measured using a spectrophotometer,
Measured by measuring the absorbance at a wavelength of 750 nm that does not contain the light
Was. That is, the dry weight of the alga body prepared in advance and the wavelength 75
From the calibration curve with the absorbance at 0 nm,
Calculated using: Dry weight (g · L^-1) = 0.362 × OD₇₅₀(OD
₇₅₀<0.3) (CO_TwoEffect of concentration, temperature of culture solution and initial pH) CO_Two
Concentration, culture temperature and initial pH affect algal growth.
The effect of this is shown in Figure 2 (the vertical line in the graph indicates the standard error).
). 5% CO_TwoOptimal conditions for algal growth
But 10% or 15% CO_TwoUnder concentration conditions
Also showed active growth, and the maximum specific growth rate decreased slightly
Degree. Thus, the chlorella separated in Example 1
(HO-1 strain) is CO_TwoNo problem regarding concentration
, That is, CO in exhaust gas_TwoCan be fixed
Was something. 35 ° C is optimal for the temperature of the culture solution
However, the maximum specific growth rates were 40 ° C and 42 ° C.
And high values at 45 ° C. As shown in Table 2, 3
Algal density after batch culture for 1 day (final algal density reached)
Also showed similar results. So far at a temperature of 40 ° C
Growing chlorella strains have been reported, but this strain
There is a 5-day lag phase before initiation (Phytochemi
stry, 31, 3345-3348, 1992)
The isolated HO-1 strain was cultured under a culture solution temperature of 40 ° C.
No induction period until the start of proliferation
Was. Propagation should start immediately even under such high temperature conditions.
Is an advantage of the isolate of the present invention. In addition, the present invention
The growth of the isolated strain was confirmed even at the temperature of 45 ° C as described above.
When the HO-1 strain is cultured outdoors,
It is very likely that culture can be performed without performing
The nature has high value when considering outdoor production
You. [Table 2] Influence of temperature of culture medium on final reached algal cell density 温度 Temperature of culture medium Final algal cells reached Density [g · L^-1] ２５ 25 ° C 1.11 ± 0.04 35 ° C 1.68 ± 0.02 40 ° C 1.24 ± 0.02 ｐＨ For the initial pH of the culture, pH 6.0 is the optimal value.
Was. When the initial pH is in the range of 4.0 to 7.0,
It had no significant effect on pH 3.0, but at pH 3.0
Had severe inhibition of growth. (NO, SO_TwoEffect) 10% CO_TwoNO for enriched air
And SO_TwoHO-1 strain
The maximum specific growth rate when batch culture was performed for 3 days
The final reached algal body density was examined. Table 3 shows the results. 10%
CO_TwoOnly case was used as control. 100
The maximum specific growth rate and maximum
The final algal cell density is at the same level as the control.
A similar change in algal body density with time was observed. This result
As a result, this Chlorella HO-1 strain is resistant to NO.
Turned out to have. 25 ppm SO_TwoAdd
When compared to the control, the maximum specific growth rate and
The final density of the algal cells reached the same value. Next, the alga body
Of the culture in the presence and absence of
SO on H change_TwoThe pH of the culture solution.
The change over time is shown in FIG. 10% if no algal body is present
CO_TwoWhen the enriched air is ventilated, the culture solution is 30 minutes after aeration.
pH drops from 6.0 to 5.0, then 5.0 laps
The value of the side was kept. In contrast, SO_TwoWhen is added
Then, the pH of the culture solution drops sharply from 6.0 to 3.0.
Was. On the other hand, when alga bodies are present, 25 ppm of SO
_TwoIs aerated, the pH of the culture solution is 6.0 30 minutes after the aeration.
From 5.0 to 5.0, after which the pH increased with time.
After 60 hours, it exceeded 6.0. PH of the culture solution
Is it impossible to grow Chlorella HO-1 strain in 3.0?
Et al., 25 ppm SO_TwoAlgae grow when air is ventilated
After the initial drop to pH 5.0, the culture broth was
It is expected that the decrease in pH could be prevented. This
For SO_Two, The pH of the culture was adjusted to 6.0.
Keeping them around is essential for the stable growth of algae.
It turned out to be a necessary condition. In addition, 100 ppm
NO and 25 ppm SO_TwoTable 3
As shown in the figure, the maximum specific growth rate and
Can obtain the same value as the control,
Showed growth. In this case, the pH of the culture solution was around 6.0.
Value was kept. From the above results, the microalgae of the present invention
And the gas to be aerated to culture the Chlorella HO-1 strain
And SO_TwoFrom LNG-fired thermal power stations
Not only SO_TwoCoal and oil fired power plants
It is clear that these exhaust gases can be used. [Table 3] Effect of NO and SO on algal growth_TwoEffect 種類 Gas type^* Maximum specific growth rate [h^-1] The final algal cell density [g · L^-1] (Mean ± standard error) (mean ± standard error) ─────────────────────────────────── A 0.115 ± 0.001 1.68 ± 0.02 B 0.110 ± 0.000 1.53 ± 0.03 C 0.109 ± 0.004 1.71 ± 0.04 D 0.111 ± 0.001 1.53 ± 0.04 mm^* The type of gas used and the concentration in the ventilated air are as follows: A: 10% CO_Two B: 10% CO_Two+100 ppm NO C: 10% CO_Two+25 ppm SO_Two D: 10% CO_Two+ 100ppmNO + 25ppmSO_Two

Example 3 Spiral tubular reactor
Cultivation of Isolates Using the Method (Experimental Method)
Investigation using spiral tubular reactor to check
Was done. Figure 4 shows an overview of the spiral tubular reactor
Shown in The reactor is a conical spiral tubular
A light receiving unit 1, a metal halide lamp 5 as a light source,
Gas supply system 7, 8, 9 for supplying gas to be aerated
It is roughly constituted from. Overflows from the upper part
The culture broth is transferred to the degassing tank 4 via the connecting tube 2.
At this point, the gas is exhausted. The culture solution is
It reaches the heat exchange tank 3 via the connecting tube 2 and is cooled.
Is returned to the lower part of the light receiving unit 1 via the connecting tube 2
You. In the figure, reference numeral 10 denotes a flush cooler. Metal Harai
The three drains 5 are arranged above the light receiving section 1.
The irradiation time and timing are controlled by the timer 6
I have. Gas supply system is air pump 7, CO_TwoGas cylinder
8 and SO (not shown)_X(SO_TwoEtc.) and NO_X(N
O) gas cylinders and flow rates to control their respective flow rates
Consists of a total of nine. The tubular light receiving section 1 has an inner diameter of 16 mm,
A vinyl chloride tube with an outer diameter of 20 mm is placed at the angle
Is spirally wound in a conical shape of about 60 °. tube
The diameter of the upper part a of the light receiving part 1 is 80 cm and the installation area is
0.5m^TwoAnd the surface area of the light receiving section is 1.0 m
^TwoIt is. 250W for metal halide lamp 5
Two types of 400W were used. Light intensity is photosynthesis
Photosynthetic Photon Flux Density:
PPFD, unit is μmol ・ m^-2・ S^-1, 400-700n
m wavelength light), the upper part of the light receiving part and the surface of the light receiving part
The average light intensity at
And 248 point measurements. 250W
In the case of a metal halide lamp, the average light intensity
The result of the measurement is 980 μmol · m^-2・ S^-1And this
Is the average solar radiation condition from April to September in the central region of Japan
Is equivalent to On the other hand, a 400W metal halide lamp
In this case, the measurement result of the average light intensity at the upper part of the light receiving unit is 1737.
μmol ・ m^-2・ S^-1Met. This value is 250W
It is about twice that of the Talhalide lamp,
Light conditions in mid-south summer. First of all, Sama
10% CO under various ventilation speed conditions_TwoEnrich air
For 6 days. NO and S
O_TwoEffect on the photosynthetic productivity of algae by the same 10%
CO_TwoIt was studied under the conditions. NO and SO_TwoVentilation is light
Only conditions were performed. In addition, 400W metal halide
The effect of strong light on photosynthetic productivity
Solid. The initial algal inoculum concentration in each experiment was 0.4g dry
Weight / L^-1And use 14L M4N liquid medium (Table 4)
Batch culture was performed every 12 hours in a light-dark cycle. Dry alga
Sampling every 12 hours to determine dry weight
The analysis was performed. Here, the measurement of the dry weight of the alga bodies was performed
The procedure was as in Example 2.After the completion of batch culture, the culture was centrifuged at 8000 rpm, 25 ° C.,
Centrifugation was performed for 5 minutes to collect algal cells. Algae collected
The body is dried at 105 ° C for 24 hours.
It was pulverized with a rod and used for analyzing the carbon content of algal cells. Algae
The carbon content of the body is measured with a CHNS / O analyzer (Perkin
-Elmer Applied Biosystems)
went. (Photosynthetic productivity of isolated algae strain) Aeration rate of 10% enriched air
The spiral tubular reactor to
Batch culture is performed using a metal halide lamp as a light source.
The results show that in each case the 12-hour provision
The photosynthetic productivity in each case, and
The maximum photosynthetic productivity per 12 hours was determined. 12
Effect of aeration rate on maximum photosynthetic productivity in bright light conditions
The effect is shown in FIG. Chlorella HO-1 strain is 0.6-5.
0L min^-1With a wide range of ventilation speeds up to
It showed high photosynthetic productivity. This chlorella has a ventilation speed of 1.
8 to 3.0 L min^-1Is the optimal range.
In the experiment below, the ventilation rate was 1.8 L min.^-1As
Study was carried out. Using a spiral tubular reactor
Of the effects of isolates on photosynthetic productivity
Are summarized in Table 5 (the light source is a 250 W metal halide
Pumps). 10% CO_TwoPlace through enriched air
If the maximum photosynthetic productivity per installation area is 34.2g dry
Dry weight / m^-2・ Day^-1Met. 100 in the enriched air
The same photosynthetic productivity is obtained when ppm NO is added.
I got it. 100 ppm NO and 25 ppm
SO_TwoTo 10% CO_TwoPhotosynthesis when added to enriched air
Productivity is 10% CO_TwoSlightly lower than when only enriched air is used
31.9 g dry weight / m^-2・ Day
^-1And a sufficiently high value. Reduce cooling operation in heat exchange tank
In this experiment, do not cool the culture solution
Grew well in all cases,
Photosynthetic productivity could be obtained. As shown in Example 2
And the optimal temperature of the HO-1 strain was 35 ° C.
Despite the maximum temperature of the liquid reached 42 ℃, active
Showed growth. About 6 hours out of 12 hours irradiation time,
Although the temperature of the culture solution exceeded 40 ° C.,
That the microalgae of the present invention was at a sufficiently high temperature.
Proven resistance. Production of HO-1 strain isolated this time
Compare sex with other culture systems. So far the following
Such productivity has been reported. Panel type reactor
24g when Spirulina is cultured in Italy using
Weight / m^-2・ Day^-1(Journal of Applied Phycolog
y, 4, 221-231, 1992); Two-tank Chu in Italy in June
When spirulina was cultured using a blur reactor
27.8g dry weight ・ m^-2・ Day^-1(Biotechnology
and Bioengineering, 42, 891-898, 1993);
Cultivate tetraselmis in open-air areas under strong light conditions
10.5g carbon weight ・ m when nourished^-2・ Day^-1(Biot
echnology and Bioengineering, 37, 936-947, 1991
 ); Spirulina cultivation using outdoor pond in Israel
20.8g dry weight ・ m^-2・ Day^-1(Plan
t, Cell and Environment, 15, 613-616, 1992)
You. HO-1 strain using spiral tubular reactor
Photosynthetic productivity obtained by culturing
It can be seen that the value is higher than that of the sample (see Table 5). In addition,
The value obtained this time is 10% CO_TwoWhen enriched air is vented
Chlorella HA-1 strain (JP-A-5-304945)
28.1 g dry weight / m^-2・ Day^-1Value
Was also exceeded. To grasp the light energy use efficiency
Needs to examine photosynthetic efficiency. Photosynthetic efficiency is
Photosynthetic Activated Radiation (Photosynthetic Activ
e Radiation, PAR) Increase relative to standard light energy
It is defined as the percentage of the energy of the alga body that is lost. Therefore
From the results obtained in the above experiment, the maximum photosynthesis
The efficiency was calculated: (a) First, the received energy per reactor was calculated as
The product of the surface area of the actor receiver and the light intensity on the receiver surface
[Where the received energy is in W · m ^-2age
In this case, W · m^-2To μmol · m^-2・
s^-14.6 when converting to a metal halide lamp
) Is used. Light receiving surface (conical)
Of average light intensity at 484 μmol · m^-2・
s^-1, Light irradiation cycle is 12h-day^-1], 4571
kJ reactor^-1・ Day^-1Get the value of (B) On the other hand, as a result of measuring the carbon content of the alga body,
Contains 8.1% carbon and biomass per carbon content
Mass energy amount is 47.7 kJ · g^-1Carbon weight
Therefore, the amount of biomass energy per alga body weight is 2
2.9kJ · g^-1It is the dry weight. Using this value,
Calculate algal energy for the increased amount. (C) dividing the value obtained in b above by the value obtained in a above
By setting it as a percentage, the maximum photosynthetic efficiency can be increased.
calculate. As a result, 10% CO_TwoVentilated enriched air
In this case, the maximum photosynthetic efficiency is extremely high at 8.64% (PAR).
It showed a high value. When 100 ppm of NO is added,
The maximum photosynthetic efficiency is 8.51% (PAR), which is 10%
CO_TwoObtain the same value as when enriched air is ventilated
Was completed. 100 ppm NO and 25 ppm SO _TwoTo
10% CO_TwoMaximum photosynthetic efficiency when added to enriched air
Was slightly lower, but still 8.05% (PAR)
It showed a high value. Thus, CO_Two, NO, SO_TwoBlend of
Photosynthetic efficiency is less than 8% (PAR) even under combined gas conditions
Was on. The photosynthetic efficiency of the HO-1 strain obtained this time is
6.6% of spirulina cultured in Thalia (PAR)
(Biotechnology and Bioengineering, 42, 891-898, 1
993) and 4.7 when Tetracellis was cultured in Hawaii.
% (PAR) (Biotechnology and Bioengineering, 37,
 936-947, 1991).
In addition, a chlorella HA-
Photosynthetic efficiency when one strain is cultured is 6.79% (PAR)
The present invention is much more than this.
From the above, the microalga of the present invention has high photosynthetic productivity.
And LNG, coal and oil fired
Exhaust gas from the substation is sent directly to the spiral tubular reactor.
It is clear that microalgae can be cultured even if they are introduced in contact
Was. [Table 5] Maximum photosynthetic productivity and maximum photosynthetic efficiency in a spiral tubular reactor using a 250 W metal halide lamp最大 Maximum photosynthetic productivity of gas^{* 2} Recovered energy^{* 3} Maximum photosynthetic efficiency^*Four type^{* 1} Per culture medium per installation area Ａ A 1.23 34.2 395 8 .64 B 1.21 33.7 389 8.51 C 1.15 31.9 368 8.05} ─────────^{* 1} The type of gas used and the concentration in the ventilated air are as follows: A: 10% CO_Two B: 10% CO_Two+100 ppm NO C: 10% CO_Two+ 100ppmNO + 25ppmSO_Two (In all cases A to C, the received light energy was 4571 kJ / reactor under 12 hours light condition.)^-1・ Day^-1Met)^{* 2} It is the maximum photosynthetic productivity per culture solution or installation area under 12 hours light conditions, and the unit is g · L.^-1・ Day^-1Or gm^-2・ Day^-1It is.^{* 3} This is the energy recovered as biomass under 12-hour light conditions, and the unit is kJ.^-1・ Day^-1.^*Four Units%. (Culture characteristics under strong light conditions)
Since the light becomes strong, the metal halide lamp needs to be 250W
To 400W for summer fine weather in Japan
Set the light conditions and use a spiral tubular reactor
10% CO_TwoBatch culture was performed with enriched air.
Adjust the maximum temperature of the culture solution under 12 hours light conditions
For this purpose, a cooling device was used in the heat exchange tank. Any
Under the conditions, the temperature of the culture solution is 1 hour after the start of light irradiation
And then rises rapidly for 5 hours
Then, the value near the maximum temperature was maintained for about 6 hours. photosynthesis
Figure 6 shows the effect of the maximum temperature of the culture solution on the productivity.
Was. Maximum photosynthetic productivity was obtained at a maximum temperature of 38.0 ° C.
Was done. Photosynthesis up to 46.5 ° C
Productivity gradually decreased with increasing maximum temperature. After that
At the above temperature, photosynthetic productivity was significantly reduced. Maximum temperature
If chlorella reaches 49.7 ° C, the chlorella can survive.
But could survive at 48.7 ° C,
Moreover, they showed proliferation. In high light conditions, a spiral tube
Table 6 shows the photosynthetic production capacity of algae using a blur reactor
Summarized in For comparison, 250W metal halide
10% CO using lamp_TwoBatch with enriched air
The results at the time of culturing are shown. As a result of the light intensity measurement,
The average light intensity on the light receiving part surface (conical type) is 889 μmol
・ M^-2・ S^-1The light receiving energy per reactor
Energy is 8391kJ reactor^-1day^-1(Light irradiation
Cycle is 12h day^-1). The maximum output is
Photosynthetic production per installation area at a maximum temperature of 38.0 ° C
Productivity is 49.9g dry weight m^-2・ Day^-1Met. This
Is converted to energy recovered as biomass
And 576kJ reactor^-1day^-1(Light irradiation cycle
Is 12h · day^-1). As a result, the summer sunny weather
The maximum photosynthetic efficiency under light conditions in the middle of the south is 6.87%
(PAR). Average solar radiation conditions in Japan (light receiving
The light intensity on the surface of the part is 484 μmol · m^-2・ S^-1time)
Was lower than the photosynthetic efficiency obtained in
It showed low and high values. In this way, high light and high temperature
That high productivity was achieved
Considering the outdoors culture of algae, it is very preferable. Book
In the experiment, strong light was continuously irradiated for 12 hours.
High light energy under strong light conditions in outdoor environments
The temperature of the cultivation medium after irradiation increases for a shorter time.
You. Therefore, when the microalga of the present invention is cultured outdoors,
It is clear that the cooling load during the season can be reduced.
You. [Table 6] Photosynthetic productivity in spiral tubular reactor ─────────────────────────────────── used Types of metal halide lamps 250W 400W ─────────────────────────────────── Light receiving energy^{* 1} 4571 8391 Maximum photosynthetic productivity^{* 2} 1.23 1.79 per culture solution 34.2 49.9 per installation area Recovery energy as biomass^{* 3} 395 576 Maximum photosynthetic efficiency^*Four 8.64 6.87 ───────────────────────────────────^{* 1} Energy received under 12-hour light conditions, in kJ reactor^-1・ Day^-1.^{* 2} It is the maximum photosynthetic productivity per culture solution or installation area under 12 hours light conditions, and the unit is g · L.^-1・ Day^-1Or gm^-2・ Day^-1.^{* 3} This is the energy recovered as biomass under 12-hour light conditions, and the unit is kJ.^-1・ Day^-1.^*Four Units%.

[0013]

As described in detail above, the present invention
Microalgae for fixing carbon oxide have high CO _TwoConcentration, NO_XDark
Degree, SO_XBecause it can grow under the concentration conditions,
Even if seed fossil fuel combustion exhaust gas is directly introduced into the culture device,
Fixes and proliferates carbon dioxide in exhaust gas
is there. In addition, even under strong light and high temperature conditions in summer,
Ming microalgae can actively grow and reduce the cooling load.
Can be planned. Furthermore, CO by the microalgae of the present invention
_TwoFixed products have high protein content and can be used for livestock feed and industrial applications.
It can be effectively used as a raw material for protein
Waste (CO in exhaust gas)_Two) Effective use
Cultivation of forests to increase feed grain production
It can halt the landslide and destroy tropical forests and deserts
Not only prevent population growth, but also increase population and
Global environmental issues, such as solving food issues caused by rising
It greatly contributes to the decision. The present invention also relates to the above book.
CO in the microalgae of the invention_TwoHigh concentration of 5-20% by volume
Of cultivation method comprising aeration of gas contained in cultivation
Enabled. NO as the gas_XAnd SO_XContains
Gas from a thermal power plant,
Not only can microalgae be cultured at low cost.
And CO_TwoAnd contributes to environmental protection. Culture tank
Use a so-called spiral tubular reactor
This makes it possible to use light energy during culture by light irradiation.
The usage efficiency can be further improved.

[Brief description of the drawings]

FIG. 1 is a transmission electron micrograph showing the morphology of an organism of HO-1 strain, which is a kind of microalgae of the present invention.

FIG. 2 is a graph showing the effects of various factors on the growth of microalgae, wherein (A) is the CO ₂ concentration, (B) is the temperature of the culture solution, and (C) is the effect of the initial pH of the culture solution. It is shown.

FIG. 3 is a graph showing the effect of SO ₂ concentration on the change over time in the pH of a culture solution.

FIG. 4 is a drawing schematically showing a conical spiral tubular reactor.

FIG. 5 is a graph showing the effect of aeration rate on maximum photosynthetic productivity under 12 hour light conditions.

FIG. 6 is a graph showing the effect of the maximum temperature of the culture solution on the maximum photosynthetic productivity.

Claims (5)

[Claims] 1. A concentration of NO _X to 200 ppm, 50p
SO _X concentration of up to pm, 1000~2000μmol ·
a microalgae capable of growing under at least one condition selected from the group consisting of a light intensity of m ⁻² s ⁻¹ and a temperature of 35 to 49 ° C. and a CO ₂ concentration of 5 to 20% by volume . 2. The microalgae according to claim 1, which is a Chlorella solokiniana HO-1 strain. 3. A method for culturing microalgae, comprising aerating a gas having a CO ₂ concentration of 5 to 20% by volume to the microalgae according to claim 1 or 2 in a culture tank. 4. The method according to claim 3, wherein the gas to be aerated is a thermal power plant exhaust gas. 5. A culture tank formed by spirally winding a colorless and transparent tube as a culture tank.
The described method.