Influence of Nitrate Feeding on Carbon Dioxide Fixation by Microalgae

다국어 초록 (Multilingual Abstract)

<P>In this study, the effects of nitrate feeding on microalgal growth and associated CO<SUB>2</SUB> fixation were evaluated, as a strategy to enhance carbon fixation by increasing the duration of the exponential phase of cell growth in the batch operation of a photobioreactor. Two species of green algae, <I>Chlorella</I> and <I>Scenedesmus</I>, and two species of cyanobacteria, <I>Microcystis ichthyoblabe</I> and <I>Microcystis aeruginosa</I>, were used after adaptation to a 15% (v/v) CO<SUB>2</SUB> environment. In the absence of nitrate feeding, nitrate concentrations declined rapidly and soon became a limiting factor. Nitrate feeding, administered in fed-batch mode to maintain 15–20 ppm of NO<SUB>3</SUB>-N, allowed for an extension of the exponential growth phase by more than 3 days, as well as a higher cell density, which subsequently resulted in an increase in photoautotrophic carbon fixation. The increases in the carbon fixation rate were in the ranges of 56.1–56.6% for the green algae, and between 68.2–68.8% for the cyanobacteria. The results indicated that intermittent nitrate feeding was a viable strategy for the augmentation of fixation productivity, and may thus be effectively applied as a substitute for conventional medium change, which has traditionally been employed in order to prolong the active growth duration.</P>