Effect of pH on Inorganic Carbon Uptake in Algal Cultures

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Abstract
Biomass production by the green algae Scenedesmus obliquus and Chlorella vulgaris in intensive laboratory continuous cultures was considerably affected by the pH at which the cultures were maintained. Carbon photoassimilation experiments revealed that pH values in the range of 8 to 9 were important for determining the free CO2 concentrations in the medium. With higher pH values, additional pH effects were observed involving a decrease in the relative high affinity of low CO2-adapted algae to free CO2. The carbon uptake rate by high CO2-adapted algae after transfer to low free CO2 medium was characterized by a lag period of about 30 min, after which the affinity of the algae to CO2 increased considerably. Both continuous growth and carbon uptake experiments indicated that artificially maintained high free CO2 concentrations are recommended for maximal production in intensive outdoor algal cultures.