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We have constructed a unit that uses microalgae to treat atmospheres containing low (i.e., (1000 ppm to 1%) concentrations of carbon dioxide. This experimental unit consists of a 20 l microalgae cultivation tank with eleven fluorescent lamps installed uniformly inside; and an analyzer with aeration/discharge, cultivation solutions supply/discharge function, and control capabilities. Using this unit, we conducted a series of experiments designed to reduce CO2 concentration in air from about 1000 ppm to atmospheric levels, and to regenerate oxygen. We used Chlorella sorokiniana ATCC22521, a species of green algae, which is said to have a relatively high growth rate. We studied a number of necessary conditions. We performed a series of experiments under various cultivation temperature conditions.

We carried out a series of experiments on the culturing of micro-algae with the intention of eliminating carbon dioxide and recovering oxygen. The reactor used for culturing photosynthetic algae (photobioreactor) was manufactured on trial; we cultured C. ellipsoidea C-27 in this photobioreactor by passing air containing about 1% CO2 at a constant irradiation intensity of 1.6 W/reactor. The daily irradiation time was set for 8, 12, and 16 hours. The findings showed that the shorter the irradiation time, the longer it took to initiate growth (the growth lag phase increased), and the maximum number of cells obtained differed as well. On the other hand, the maximum growth rate remained almost unchanged, and the energy required for growth was accumulated in the cells regardless of the average daily dose of irradiation.

Clam is a kind of bivalve mollusks, having a high nutritive value and good taste. A combination of clams and food plant should provide a balanced diet. The cultivating module mainly consists of a clam cultivating unit, a microalgae cultivating unit and water recycle system including a water reclamating unit, a solid waste treatment unit like wet oxidation, a water sterilizing unit and a salinity adjusting unit. Recycled water from the water reclamating unit is supplied to the clam cultivating unit and the microalgae cultivating unit after being sterilized. Concentration of salts in the water must be adjusted by salt supplied from a mineral recovery unit in habitat module. Lost water and nutrient required for microalgae cultivation must be supplied from habitat module or plant cultivating module. Lipid profile and optimum cultivating condition of several microalgae were investigated. Total fatty acid contents of marine microalgae were higher than those of freshwater microalgae.

Prototype bioreactor using internal lighting mechanism was manufactured for biological CO2/O2 conversion system. Microalgae culturing experiments were carried out on Chlorella ellipsoidea C-27 to estimate the effect of light intensity on photosynthetic activity in the reactor. The light energy source used was an Xe(xenon) lamp, from which light is transferred through optical fibers and diffused from the surface of rods made of acrylic resin. Total surface area of the rods was 0.12m2. Tests under the continuous lighting (600W) condition indicated a highest specific growth rate of 8.54 (h-1), a highest cell density of 1.3 × 108 (cells/ml), and a maximum overall photosynthetic rate (CO2 absorption rate) of 171.84 (mg-CO2 absorption/Ir-medium/day). In contrast, the maximum CO2 absorption per chlorophyll content (mg-CO2 absorption/mg-chl/h) was reached under the alternating lighting condition.