Simple method for measuring the spectral absorption cross-section of microalgae Razmig Kandilian, Antoine Soulies, Jeremy Pruvost, Benoit Rousseau, Jack Legrand, Laurent Pilon To cite this version: Razmig Kandilian, Antoine Soulies, Jeremy Pruvost, Benoit Rousseau, Jack Legrand, et al.. Simple method for measuring the spectral absorption cross-section of microalgae. Chemical Engineering Science, Elsevier, 2016, 146, pp.357-368. 10.1016/j.ces.2016.02.039. hal-01949492 HAL Id: hal-01949492 https://hal.archives-ouvertes.fr/hal-01949492 Submitted on 20 Apr 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Chemical Engineering Science 146 (2016) 357–368 Contents lists available at ScienceDirect Chemical Engineering Science journal homepage: www.elsevier.com/locate/ces Simple method for measuring the spectral absorption cross-section of microalgae Razmig Kandilian a,b, Antoine Soulies b, Jeremy Pruvost b, Benoit Rousseau c, Jack Legrand b, Laurent Pilon a,n a Mechanical and Aerospace Engineering Department, Henry Samueli School of Engineering and Applied Science, University of California, 420 Westwood Plaza, Eng. IV 37-132, Los Angeles, CA 90095, USA b Université de Nantes, GEPEA CNRS, UMR 6144, Bd de l'Université, CRTT - BP 406, 44602 Saint-Nazaire Cedex, France c Laboratoire de Thermocinétique de Nantes, Université de Nantes, UMR CNRS 6607, Nantes, France HIGHLIGHTS A simple procedure for measuring microalgae spectral absorption cross-section is proposed. It is based on normal–hemispherical transmittance and reflectance measurements. It was validated against direct measurements of the radiation characteristics of C. vulgaris. It can be used for other suspensions of absorbing and scattering particles. It can be used to predict and control light transfer and biomass productivity in PBRs. article info abstract Article history: The spectral absorption cross-section of microalgae is an essential parameter in modeling the microalgae Received 15 October 2015 metabolism and growth kinetics as well as in estimating the productivity and efficiency of photo- Received in revised form bioreactors. This paper presents a simple experimental procedure for retrieving the average spectral 16 February 2016 absorption cross-section of concentrated microalgal suspensions. The method combines experimental Accepted 23 February 2016 measurements of the normal–hemispherical transmittance and reflectance of the suspensions in con- Available online 3 March 2016 ventional cuvettes with an inverse method and analytical expressions obtained from the modified two- Keywords: flux approximation accounting for absorption and multiple scattering. The method was validated with Light transfer direct measurements of the scattering phase function and of the absorption and scattering cross-sections Photobioreactors of freshwater microalgae Chlorella vulgaris. It was able to retrieve the absorption cross-section with Light absorption acceptable accuracy. The latter was then used to estimate successfully the fluence rate using a simplified Microalgae fl Growth modeling light transfer model, the local rate of photon absorption, and the biomass productivity in at plate PBRs. & 2016 Elsevier Ltd. All rights reserved. 1. Introduction photosynthetic microorganisms (Cornet et al., 1998; Pilon et al., 2011). Illumination conditions within the culture can vary strongly with time Cultivation of photosynthetic microorganisms has received sig- depending on the season, on the local weather, and on the photo- nificant interest in recent years as a way to produce a broad range of adaptation of the microorganisms which reduces or increases their chemical compounds including food supplements, fertilizers, hydro- pigment concentrations under excessive illumination or light limiting gen gas, and lipids for biodiesel production (Richmond, 2004). A wide conditions, respectively. Physical modeling coupling light transfer to variety of microalgae and cyanobacteria species can be cultivated in growth kinetics and metabolic activities can facilitate the optimum design, operation, and control of photobioreactors (Cornet et al., 1992, fresh or brackish waters as well as in seawater. Cultivation typically 1992, 1995; Cornet and Dussap, 2009; Murphy and Berberoğlu, 2011; takes place in outdoor raceway ponds or photobioreactors. Light Pilon et al., 2011; Takache et al., 2010, 2012; Pruvost et al., 2012; transfer in such systems is arguably one of the most important Wheaton and Krishnamoorthy, 2012; Kandilian et al., 2014; Kong and parameters affecting both the growth rate and metabolism of the Vigil, 2014). To do so, knowing the radiation characteristics of microalgae and the amount of light they absorb to drive the photo- n Corresponding author. Tel.: þ1 310 206 5598; fax: þ1 310 206 2302. synthesis is essential. In fact, the radiation characteristics of micro- E-mail address: [email protected] (L. Pilon). organisms vary significantly among species (Berberoğlu and Pilon, http://dx.doi.org/10.1016/j.ces.2016.02.039 0009-2509/& 2016 Elsevier Ltd. All rights reserved. 358 R. Kandilian et al. / Chemical Engineering Science 146 (2016) 357–368 ğ μ μ ¼ μμ0 þ 2007; Berbero lu et al., 2008; Heng et al., 2014) or during the culti- geometrical consideration, 0 can be expressed as 0 = = vation process. This is particularly true during nitrogen starvation ð1Àμ2Þ1 2ð1Àμ02Þ1 2 (Modest, 2013). used to trigger lipid accumulation (Kandilian et al., 2013; Heng et al., In cases when scatterers are much larger than the radiation 2014; Heng and Pilon, 2014; Kandilian et al., 2014). wavelength, scattering is mainly forward and the scattering phase The goal of the present study is to develop a simple yet accu- function can be estimated based on the transport approximation ðμ Þ¼ À þ δð Àμ Þ rate experimental method for determining the spectral absorption as pλ 0 1 gλ 2gλ 1 0 (McKellar and Box, 1981). Here, cross-section of microalgae over the photosynthetically active δðμÞ is the Dirac delta function and gλ is the asymmetry factor at radiation (PAR) region, corresponding to wavelength between 400 wavelength λ defined as and 700 nm. This method does not require the knowledge of the Z 1 scattering phase function of the microorganisms or the use of a ¼ 1 ðμ Þμ μ : ð Þ gλ pλ 0 0 d 0 3 nephelometer, which can be costly and difficult to operate. 2 À 1 Moreover, it only requires an integrating sphere spectro- Then, the RTE can be expressed as photometer. It also aims to demonstrate that the use of the Z fi ∂ σ 1 absorption cross-section alone with a simpli ed light transfer μ Iλ ¼ðκ þσ Þ þ s;tr;λ ðμ0; Þ μ0 ð Þ fi ∂ λ s;tr;λ Iλ Iλ z d 4 model is suf cient to predict light transfer, growth kinetics, and z 2 À 1 biomass productivity of PBRs. The unicellular microalgae Chlorella σ ¼ð À Þσ fi vulgaris was used to illustrate the new method because of the where s;tr;λ 1 gλ s;λ is the transport scattering coef cient. interest in the wide range of compounds it can produce. In the context of light transfer in photobioreactors, the absorption and scattering coefficients are linearly proportional to 3 the number density NT of the microalgae cells (in #/m ) and 2. Background expressed as κ ¼ σ ¼ ð Þ λ C abs;λNT and s;λ C sca;λNT 5 2.1. Chlorella vulgaris 2 where C abs;λ and C sca;λ (in m ) are the average spectral absorption Chlorella vulgaris is a unicellular microalgae with spherical and scattering cross-sections of a cell, respectively. Alternatively, shape and 1–6 μm in diameter (Safi et al., 2014). This particular the biomass concentration of the microalgal suspension X, species of green microalgae has garnered special attention for its expressed in mass of dry weight per unit volume (g/L or kg/m3), is large areal biomass productivity and its relatively short cell dou- κ σ often measured instead of NT. Then, one can express λ and s;λ as bling time (Griffiths and Harrison, 2009). In addition, it has been κ ¼ σ ¼ ð Þ identified as a potential source of protein for human and animal λ Aabs;λX and s;λ Ssca;λX 6 feed (Tokuşoglu and Ünal, 2003). It is also an important source for the commercial production of carotenoids and various bio- where Aabs;λ and Ssca;λ are the average spectral mass absorption 2 pharmaceuticals (Mendes et al., 2003). It can also produce lipids to and scattering cross-sections expressed in m /kg dry weight. be converted into biodiesel (Brennan and Owende, 2003). Finally, Typically, the biomass concentration X in conventional PBR vary 3 this freshwater species can be cultivated in wastewater for from 0.1 to 2.0 kg/m (Takache et al., 2010). simultaneous wastewater treatment and production of value- added products (Feng et al., 2011). 2.3. Fluence rate 2.2. One-dimensional radiative transfer equation The local spectral fluence rate GλðzÞ in a PBR is defined as the irradiance incident at location z from all directions. It is expressed 2 2 Fig. 1 shows a schematic of a microalgae suspension of thick- in W/m μmorμmolhν=m s μm and defined, in 1D radiation ness ℓ illuminated with collimated, unpolarized, and normally transfer, as incident light