Forced light/dark circulation operation of open pond for microalgae cultivation

Open pond has been widely used for microalgae culture. However its lower biomass productivity damaged its economic viability used as cultivation systems for feedstock production. In this study we introduced a forced L/D circulation operation to conventional open pond, in which the culture medium was pumped to circulate between an illuminated shallow pond and a fully darkened tank. The growth of microalgae was dominated by the photic retention time and dark/light ratio of the forced L/D circulation. The optimal values were determined to be 3.98 for dark/light ratio and 5.80 min for photic retention time by response surface methodology, at which, a biomass productivity of 36.5 g m−2 d−1 for Scenedesmus dimorphus was approached in laboratory. Outdoor cultivation practice with the forced light/dark circulation of pond was also carried out and averaged 28.5 g m−2 d−1 biomass productivity was achieved, which is double of that by conventional open pond cultivations in 250 mm or 50 mm water depth without forced circulation.