Optical extinction characteristics of three biofuel producing microalgae determined by an improved transmission method

The optical extinction characteristics of the three kinds of microalgae Nannochloropsis maritima, Ellip-soidion sp. (277.03), and Dunaliella tertiolecta were determined using an improved transmission method, in the 300-1800 nm spectral range. These three microalgae are promising candidates for the production of biofuels such as bio-hydrogen and biodiesel. The improved transmission method determines the spectral extinction coefficient of the microalgae. This is based on the measured transmittance, and employs an optical model that takes into consideration multiple reflections and refractions at the air-glass and glass-liquid interfaces. Silicon dioxide microspheres of monodisperse size were used as a model to verify the proposed method. The optical constants of the culture medium, size distributions, and extinction cross-sections of the microalgae cells were measured and analyzed. The improved transmission method is demonstrated to yield more accurate results than the traditional method. The spectral extinction efficiencies of the three kinds of microalgae show significant differences in the near ultraviolet and visible spectral regions. The spectral extinction efficiencies also exhibit small differences in the longer wavelength range of 950-1800 nm, with values generally less than 1.0. The measured extinction characteristics data of the three microalgae and the presented measurement method will facilitate process modeling in photobioreactors for biofuel production. (C) 2016 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.