A theory of photobioreactor design is developed. A photobioreactor was constructed in the form of a loop made from 52 m of glass tubing of 1 cm bore; the loop covered about 0.5 m2. The culture was illuminated with mercury halide lamps to reproduce sunlight. Computer control was used to maintain constant biomass concentration. The influence of radiation on the reactor temperature is quantitatively predicted. An air lift system was preferred to a liquid pump for culture recycle. The energy required for culture recycle in the loop with Reynolds number 2000 was 0.6 W m-2. The COZ gas/liquid transfer rate achieved was sufficient to meet the maximum possible demand with solar irradiation. The 0 2 gas/liquid transfer rate was sufficient to meet the maximum respiration demand at night. The maximum algal biomass concentration achieved exceeded 20 g dry weight litre-l. A biomass concentration of 8 g dry weight litre-1 was found to be convenient for normal operation. The maximum uptake of light in the available wavelength range (400-700 nm) was 38 W m-2, this corresponds to utilisation of solar irradiation up to 89 W m-2. Below the maximum light uptake rate the efficiency of storage of light energy in the biomass corresponded to 16.6% of solar energy.
An on-line computer was used to control the ratio of carbon to nitrogen in algal biomass. An indirect method of growth and biomass estimation was utilized. This was based on balancing the amount of CO(2) carbon in and out of the algal bioreactor. It was shown that growth conditions govern the morphology and composition of Spirulina platensis. Cells grown under light limitation were narrower, had high levels of phycocyanin pigments, and were packed full of small lipid granules. Whereas cells grown under nitrogen limitation lost their characteristic blue-green color, had reduced levels of phycocyanin, were fatter, and were packed full of larger lipid granules.
The maximum biomass in iron-limited photosynthetic batch cultures of chlorella increased as the logarithm of the iron concentration. The growth yield from iron (UxFe) showed a marked inverse relation to the specific growth rate. The maximum biomass yield, g dry biomass/g iron consumed, was 7.5 X 10(3) with specific growth rate 0.108h-1; the minimum was 0.79 X 10(3) with specific growth rate 0.145 h-1. The maximum specific growth rate in the exponential phase of Fe limited cultures varied as the initial Fe concentration. Fe-limited growth made the cells adhere to a glass surface.
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