Biotechnological investigation of Pediastrum boryanum and Desmodesmus subspicatus microalgae species for a potential application in bioenergy

Abstract

The production of photosynthetic microalgae is a promising ecological advantage for obtaining carbon credits. This paper addresses cultivation and preparation, growth analysis, physicochemical characterization (X-ray diffraction-XRD, Fourier transform infrared-FTIR, scanning electron microscopy-SEM, and energy dispersive spectroscopy-EDS), and thermal behavior (thermogravimetry-TG, derivative thermogravimetry-DTG, and differential scanning calorimetry-DSC) of two microalgae, namely Pediastrum boryanum-PB (CH007) and Desmodesmus subspicatus-DS (AEE431E) for a potential application as an energy resource. Regarding the former, the literature reports no specific study on the species, which shows high lipid productivity and fast growth. A synthetic culture medium (Walter culture-WC) was subjected to variations in pH, luminosity, and maximum growth reached in 12 and 13 days for PB and DS, respectively. TG/DTG curves identified the main thermal degradation stages, i.e., dehydration (DS (24.68–158.68 °C) and PB (20.06–116.18 °C)), devolatilization (DS (166.34–543.00 °C) and PB (128.22–493.93 °C)), and gasification or carbonization (DS (>550 °C) and PB (>500 °C)), and DSC curves revealed two endothermic events, an exothermic one for DS, and only one endothermic event and an exothermic one for PB. XRD patterns showed a cellulose crystallinity index (CI) for DS (22.54 %) and PB (28.82 %), confirming the predominance of amorphous regions. SEM images detected external epidermis for DS and some interconnected pores for PB. The FTIR spectra identified functional groups (lipids, proteins, and carbohydrates) and CO, CO, OH, CH, and C-O-C linkages, and EDS and ICP-OES identified the main organic, inorganic, and metallic elements. The microalgae species displayed characteristics similar to those of the other biomasses in the bioenergy industry, enabling their use in thermoconversion processes for biofuel production and considering some socioenvironmental aspects.