Dragone, Giuliano

Gianesella, Sonia M. F

Mesquita, Sara

Sparagna, Patricia

Teixeira, J. A.

Vicente, A. A.

Universidade do Minho: RepositoriUM

 OPTIMIZATION OF MICROALGAL BIOMASS HARVESTING  USING FERRIC CHLORIDE AS FLOCCULANT  Patricia Sparagna1, Sara Mesquita2, António A. Vicente2, José A. Teixeira2, Sonia M. F. Gianesella1, Giuliano Dragone2*  1Instituto Oceanográfico, Universidade de São Paulo, São Paulo. 05508-120, São Paulo, Brasil 2IBB - Institute for Biotechnology and Bioengineering, Centre of Biological Engineering, University of Minho. 4710-057, Braga, Portugal.  *gdragone@deb.uminho.pt  Key words: Chlorella vulgaris, flocculation, microalgae  Introduction. Microalgae are considered as one of the most promising renewable feedstock for biofuel production due to their high photosynthetic efficiency, rapid growth rates and potential for higher oil production per acre than other energy crops (1). Evaluation of several harvesting methods showed that the most promising cost and energy efficient dewatering strategy will most likely utilize microalgal flocculation as an initial concentrating step (2). The objective of this work was to optimize the flocculation efficiency of Chlorella vulgaris under different concentrations of flocculant (ferric chloride) and pH, by using response surface methodology.  Methods. The freshwater microalga C. vulgaris (strain P12) was used in this study. Cultures were grown at room temperature and 24 h illumination was provided by fluorescent light at 100 µmol/m2 s1 until they reached stationary phase.  A 22 full-factorial face-centered central composite design (CCD) was performed as a screening experiment to determine the effect of media pH and flocculant concentration on flocculation efficiency (dependent variable). Flocculant concentration and pH were tested at two levels: i) concentration of ferric chloride (FeCl3): 100 mg/L and 500 mg/L, and ii) pH: 7.0 and 13.0. Flocculation efficiency of microalgae was calculated by using the following equation: Flocculation efficiency (%) = (1 – (A-B)/(C-D)) × 100      (1) where A represents the OD750 of sample, B is the OD750 of blank (flocculant with H2O), C refers to the OD750 of control and D to the OD750 of water.  Results. Results showed that flocculation efficiency of C. vulgaris varied under the different harvesting conditions (Table 1). The highest value of biomass recovery (98.1%) was obtained when the flocculation process was performed by using 300 mg/L FeCl3 at pH 10. The experimental values were fitted to a second-order equation obtained by multiple regression analysis. The three-dimensional response surface described by the model equation was depicted in Figure 1. An estimate of the critical point revealed that biomass harvesting can be maximized by using 412 mg/L FeCl3 at pH 9.1.  Assays for validation of this model were then performed under the established optimal operating conditions and the obtained value of flocculation efficiency was 98.5%.    Table 1. Flocculation efficiency of C. vulgaris under different pH and flocculant concentration according to the full CCD.                               Fig.1 Response surface of flocculation efficiency of C. vulgaris as a function of pH and concentration of ferric chloride.  Conclusions. Best flocculation conditions were achieved by using 412 mg/L ferric chloride at pH 9.1.  Acknowledgements. Fundação para a Ciência e a Tecnologia (SFRH/BPD/44935/2008), CNPq (Ciência sem fronteiras program) and projects INNOVALGAE (FCT PTDC/AAC-AMB/108511/2008) and ALGANOL.  References. 1. Dragone G., Fernandes B., Vicente A., Teixeira J.A. (2010). Third generation biofuels from microalgae. In: Current Research, Technology and Education Topics in Applied Microbiology and Microbial Biotechnology. Vilas A.M.  Formatex Research Center, Badajoz. 1355-1366  2. Molina Grima E., Belarbi E.H., Acién Fernández F.G., Robles Medina A., Chisti Y. (2003). Biotechnol Adv. vol(20.): 491-515. Concentration (mg/L) pH Efficiency (%) 300 10 98.0 100 7 53.3 300 10 98.1 300 10 97.5 300 10 97.4 300 13 86.0 500 10 94.9 300 7 95.4 500 7 97.5 100 13 62.7 500 13 92.7 100 10 62.7 300 10 98.1 300 10 97.5 

Optimization of microalgal biomass harvesting using ferric chloride as flocculant

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Universidade do Minho: RepositoriUM

Universidade do Minho: RepositoriUM