Abstract
Microalgae perform photosynthesis at a high efficiency under low light conditions. However, under bright sunlight, it is difficult to achieve a high photosynthetic efficiency, because cells absorb more light energy than can be converted to biochemical energy. Consequently microalgae dissipate part of the absorbed light energy as heat. The objective of this study was to investigate photobioreactor productivity as a function of the biomass specific light absorption rate. A strategy to circumvent oversaturation is to exploit light with a spectral composition that minimizes light absorption. We studied productivity of Chlamydomonas reinhardtii cultivated under different colors of light. The incident light intensity was 1500μmolphotonsm−2s−1, and cultivation took place in turbidostat controlled lab-scale panel photobioreactors. Our results demonstrate that, under mass culture conditions, productivity and biomass specific light absorption are inversely correlated. The highest productivity, measured under continuous illumination, was obtained using yellow light (54gm−2d−1) while blue and red light resulted in the lowest light use efficiency (29gm−2d−1). Presumed signs of biological interference caused by employing monochromatic light of various wavelengths are discussed. This study provides a base for different approaches to maximize productivity by lowering the biomass specific light absorption rate.
Highlights
Microalgae are an attractive source for biofuels and bulk chemicals due to their high photosynthetic efficiency (PE)
We presented areal biomass productivities of high density microalgae cultures exposed to high light intensities of different colors
Under mass culture conditions, biomass productivity and the biomass specific light absorption rate are inversely correlated as oversaturation of the photosystems leads to a waste of light energy and, a lower biomass yield on light
Summary
Microalgae are an attractive source for biofuels and bulk chemicals due to their high photosynthetic efficiency (PE). Maximum PE values, as measured under low light conditions, will never be realized in microalgae mass cultures exposed to direct sunlight. In a high density microalgae culture, most sunlight energy is absorbed in a small volume fraction of the photobioreactor on the light-exposed side. In this volume fraction, cells are coerced to absorb more light energy than the amount that can be converted to biochemical energy by their photosynthetic machinery. Cells are coerced to absorb more light energy than the amount that can be converted to biochemical energy by their photosynthetic machinery This leads to oversaturation and, waste of sunlight energy through heat dissipation [5]. The result is a PE that is dramatically lower than that which can be obtained under low light conditions [6]
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