JPH0412955B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing hydrogen using cyanobacteria using a light-dark cycle. In recent years, hydrogen has attracted attention as a clean energy source that can replace fossil fuels such as oil and coal. Hydrogen energy (1) can be converted into electrical energy with high efficiency using fuel cells, (2) has a calorific value per unit weight that is 3 to 4 times that of oil, and even when combusted. (3) Water, which is a raw material, is almost inexhaustible.
It has the following characteristics. Attempts to produce such hydrogen using solar energy are underway using both abiotic methods such as water splitting using semiconductors and biological methods using photosynthetic organisms. Regarding the latter biological method, there are systems that produce hydrogen through biological photolysis of water by controlling the metabolism of higher plants and algae that have the ability to decompose water, or by combining them with microorganisms that have the ability to generate hydrogen. Proposed. However, in conventional systems, oxygen generated as a result of water splitting deactivates or inhibits the hydrogen generation system (hydrogenase), becoming the main cause of instability, and the separation and purification of hydrogen is complicated. It cannot be said to be a practical hydrogen production method because there is a risk of explosion of the hydrogen-oxygen mixed gas. The present inventors conducted research to develop a biological hydrogen production method with excellent productivity and sustainability. As a result, in a specific system, the generation of oxygen and the generation of hydrogen can be temporally separated. They discovered that hydrogen can be efficiently produced by this method and completed the present invention. That is, the gist of the present invention consists of alternately repeating a cycle of culturing cyanobacteria capable of hydrogen generation in water under light aerobic conditions and a cycle of culturing them in water under dark microaerobic conditions. Hydrogen produced by cyanobacteria using a light-dark cycle, which is characterized by photosynthesizing during cultivation under aerobic conditions and decomposing substances accumulated through photosynthesis during cultivation under dark microaerobic conditions to generate hydrogen. It depends on the production method. The cyanobacteria used in the present invention may be any species as long as they have hydrogen-generating ability, but Synechococcus sp. is particularly preferred. Cyanobacteria in any growth phase can be used, but the amount of hydrogen produced under dark microaerobic conditions (hereinafter referred to as dark hydrogen production) increases.
Those in the logarithmic growth phase, particularly in the mid-logarithmic growth phase, are preferably used. In the method of the present invention, organic matter such as cyanobacteria starch is accumulated within the cells due to photosynthesis during cultivation under light aerobic conditions, and organic matter accumulated during cultivation under dark microaerobic conditions is decomposed. Hydrogen is generated. Cultivation under light and aerobic conditions is carried out in a medium containing appropriate inorganic components under light irradiation and with aeration. The culture temperature varies depending on the type of blue-green algae used, but is usually preferably 15 to 70°C. In the ventilated air, 2~
It is preferable to mix 5% by volume of carbon dioxide because it increases the amount of organic matter such as starch accumulated. Examples of suitable media include Detmer modified medium or BG-11 medium. Their compositions are shown in the table below.

【table】

【table】

[Table] Cultivation under dark microaerobic conditions is carried out in a nitrogen atmosphere containing a trace amount of oxygen, with light blocked. The temperature is preferably around the optimal growth temperature of the blue-green algae used. The amount of oxygen contained in the nitrogen atmosphere varies depending on the culture conditions, but if it is too large, it will inhibit the hydrogen generation system and is undesirable, so it is usually preferable not to exceed 0.1% by volume. It is preferable to include oxygen in the gas phase in an amount not exceeding 0.30% by volume, particularly not exceeding 0.23% by volume, at the start of cultivation under dark conditions, since this increases the rate of dark hydrogen generation. Furthermore, the amount of dark hydrogen generated increases by stirring or shaking the medium. Although the light-dark cycle can be created artificially, it is appropriate to match it to the day-night light-dark cycle. The method of the present invention not only makes it possible to produce hydrogen very economically and efficiently using solar energy, but also collects cyanobacteria that proliferate under light conditions and uses them to produce useful substances such as biomass. It is also possible. Next, examples will be shown to specifically explain the method of the present invention. Example Culture under light conditions Unicellular thermophilic cyanobacteria (Synechococcus sp.) isolated from Beppu Onsen were cultured in BG-11 medium (PH7.0).
It was added to one flask containing 500 ml and cultured and grown under fluorescent light irradiation. The flask was shaken reciprocally at 100 rpm in a constant air chamber maintained at 45°C. Dark Hydrogen Generation When the algae concentration reached approximately 20 μg drywt./ml, the algae were collected by centrifugation, washed twice with BG-11 medium, and then resuspended in 10 ml of the same medium. The algae concentration at this time was 0.17 mg/ml. The suspension was placed in a light-shielded test tube (inner volume: 34 ml) and sealed with a rubber stopper. The gas phase was replaced with nitrogen gas and a small amount of oxygen was added via syringe. Reciprocating shaking at 100 rpm was applied in a constant temperature bath at 45°C. At 2, 6.5, 12, and 20 hours after the start of shaking, 500μ samples of the gas phase were taken, and the composition was determined by gas chromatography. The results are shown in Table 4.

[Table] When the gas phase oxygen concentration was 0.08% by volume, no hydrogen generation was observed even after 20 hours, but when the oxygen concentration was 0.3% by volume, hydrogen generation was observed from around 6.5 hours, and then Hydrogen evolution continued for at least 10 hours.

Claims (1)

[Scope of Claims] 1. A method consisting of alternately repeating a cycle of culturing cyanobacteria capable of hydrogen generation in water under light aerobic conditions and a cycle of culturing them in water under dark microaerobic conditions. Hydrogen production by cyanobacteria using a light-dark cycle characterized by photosynthesis during cultivation under atmospheric conditions and decomposition of substances accumulated through photosynthesis during cultivation under dark microaerobic conditions to generate hydrogen. Method. 2. The hydrogen production method according to claim 1, wherein a mixed gas of air and carbon dioxide is aerated into the water during cultivation under light and aerobic conditions. 3 The volume ratio of carbon dioxide and air is 0:100 to 10:
90. The hydrogen production method according to claim 2, wherein the hydrogen production method is 90. 4.Culture under dark microaerobic conditions is initiated in the presence of not more than 0.30% by volume of oxygen in the gas phase, and is carried out in a nitrogen atmosphere containing a trace amount of oxygen.Claim 1
Hydrogen production method described in section. 5. The hydrogen production method according to claim 1, using cyanobacteria in the logarithmic growth phase. 6. The hydrogen production method according to claim 5, using cyanobacteria in the mid-logarithmic growth phase. 7 Cyanobacteria are of the genus Synechoccus (Synechoccus).
sp.), the hydrogen production method according to claim 1, 5 or 6. 8. The hydrogen production method according to claim 1, wherein the culture temperature in each cycle is 15 to 60°C. 9. The hydrogen production method according to claim 8, wherein the culture temperature in each cycle is 40 to 55°C. 10. The hydrogen production method according to claim 1, wherein the culture is carried out under dark microaerobic conditions with stirring or shaking. 11. The hydrogen production method according to claim 1, wherein the light/dark cycle is a day/night cycle.