The present study aims to retrieve the spectral real part (or refraction index) and imaginary part (absorption index) of the complex index of refraction of microalgae from experimentally measured size distribution as well as absorption and scattering cross-sections. The green algae
In the present study, the different microalgae were assumed to be spherical. This assumption simplifies the calculations of their radiation characteristics by using the Lorenz–Mie theory instead of the T-matrix method. Moreover, despite their heterogeneous structure, microalgae were treated as homogeneous with some effective refraction and absorption indices. The different microalgae were treated as homogeneous spheres with an equivalent diameter such that their surface area was identical to that of their actual spheroidal shape assumed to be axisymmetric. The equivalent diameter of the sphere having the same surface area as the spheroid is given by where where d and _{s}d+d_{s}d The denominator on the right-hand side is the total cell concentration _{s}.N expressed in total number of cells per m_{T}^{3} of suspension. The Lorenz-Mie theory predicts the absorption and scattering cross-sections denoted by C_{abs,}_{λ} and C_{sca,}_{λ} (expressed in m^{2}) of an individual spherical cell of diameter dwith complex index of refraction _{s }n_{λ } + ik_{λ } submerged in phosphate buffered saline (PBS) solution with refraction index n_{PBS}. Then, the absorption coefficient κ and scattering coefficient_{λ} σ of a microorganism suspension with size distribution _{s,λ}N(d) is expressed as _{s}Here, C
Fig. 2 compares the effective refraction and absorptio nindices of C. reinhardtii CC 125 and its truncated chlorophyll antenna transformants tla1, tlaX, and tla1-CW+ between 400 and 750 nm. Overall,
Fig. 3 shows the retrieved effective refraction and
absorption indices for B. braunii, Chlorella sp., and C.
littorale between 400 and 750 nm from the measured absorption and scattering cross-sections. Their refraction index n
This study presented and used a methodology to retrieve the spectral refraction and absorption indices of various biofuel producing microalgae from experimentally measured average absorption and scattering cross-sections between 400 and 750 nm. The microalgae were treated as spherical particles with equivalent diameter distributions calculated from experimentally measured major and minor diameter distributions. An inverse method was developed combining Lorenz-Mie theory as the forward method and genetic algorithm. The retrieved refraction and absorption indices were continuous function of wavelength with apparent absorption peaks corresponding to those of Chl
E. Lee, R.-L. Heng, and L. Pilon, 2013. H. Berberoğlu, L. Pilon, and A. Melis, 2008. |